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  • Writer's pictureAnthony Stevens

The Karst and the Curious

2023 Istria 100 by UTMB Blue Course: 15 April 2023

It’s been 30 years since I last visited Croatia – back when Croatia was still part of the old Yugoslavia. I’ve always been curious to see how the country has changed since then, and running Croatia’s most famous ultramarathon, the Istria 100, provided a great opportunity to do so. I was also excited to get some running in among the famous limestone Karst formations of the Eastern Alps and Balkans, given that the term “karst” originated from the ancient name for this region – amazing to think that this region now gives its name to geological formations across the world including the famous karsts of Guilin in China, Ha Long Bay in Vietnam and Sorak-San in Korea. Plus of course the famous karsts of the Dolomites, which would feature in one of the races in my schedule for later in year, the Lavaredo Ultra Trail.

Before the race

I was running the “blue” 110km course rather than the “red” 100 mile / 160 km one, mainly because with the 100 mile and 10,000m vertical Ultra Trail Snowdonia (UTS) just around the corner in May, I wanted to avoid generating too much fatigue and negatively impacting the final few weeks of training for Wales. 110km would strike the balance between being a good workout in its right as well as solid preparation for the longer distance next month. My wife and I had also decided to take an extra 4 days after the race to visit Plitvice and Krka National Parks, so I also wanted to avoid negatively impacting that as well! With that it mind, we had decided to fly to Split and rent a car from there, which meant on the day before the race having a 4am start, a 6am flight and then a 6 hour drive to get to Umag on the west coast of Istria, just across the border from Slovenia and only a few miles from Trieste in Italy. Luckily, the registration process was extremely efficient, and now with the Istria races being part of the UTMB stable, it also gave me a good idea what to expect at the other UTMB World Series races coming up on my schedule – UTS and Lavaredo.

Our hotel was right in the centre of Umag, only a 5 min walk from both the registration centre the finish line, which while it complicated parking made life much easier in terms of sorting out my drop bag and getting the bus transfer at 5.15am on the Saturday morning. For the 110km course, the race would start in Buzet, the so-called “truffle capital of Croatia”, with an initial 41km loop around the mountains of Eastern Istria, returning to Buzet where we would be able to access our drop bag at CP3, before proceeding across the peninsula towards the finish back at Umag. The drop bag itself was huge (30 litres) and easily accommodated both spare clothes as well as additional food supplies and emergency medical items such as blister plasters, chafing cream etc.

After some of the problems I’d experienced with fuelling and chafing at TransGranCanaria, I had tweaked a few things in my overall setup. With fuelling, I had been experimenting on some recent long runs with the PrecisionFuel and Awesome Sauce gels, which provided 90g and 45g respectively of carbs in easy-to-absorb and no-too-sweet formats, and I found them much easier to get down than the mix of flapjacks and chocolate I had used in Gran Canaria. Also, all UTMB races now at each checkpoint provide electrolytes / energy products from a Canadian company, Näak, and having tried some of their products at their advertising stand while registering, I figured that I could fill out the rest of the 100g / hour of carbs I estimated I needed by combining their drinks with my own MountainFuel powders at every CP and grabbing the occasional energy bar or banana. With respect to chafing, while GurneyGoo provides great lubrication protection for sensitive areas, I’ve also discovered that combining it with Germoloids ointment (which has both zinc oxide and a mild topical analgesic) can eliminate pretty much all the discomfort – astonishing and mildly embarrassing, but what works, works.

Start to CP3 Buzet

One of the upsides about catching a 6am flight the previous morning was that I was pretty tired by Friday evening, so after watching the sunset with my wife on the Umag waterfront and having a plate of truffle-laden pasta, I had no difficulty falling asleep and getting enough rest to feel fresh when I woke at 4am on Saturday to get ready for the race.

Sunset in Umag the night before the race

Everything was going smoothly as after an hour’s drive we pulled into Buzet and disembarked from the bus. I’d had a couple of cereal bars and canned coffee to top up my pre-race fuelling. A DJ was playing a thumping music set and getting everyone emotionally fired up as well. We still had 40 minutes before the race, so I did some stretches while carrying out a final check of all my kit. The internal battery on my Garmin GPS watch has been through so many charging cycles that when I use it for navigation the charge only lasts for around 6 hours, so I know make a point of carrying a small power bank and a charging cable that allows me to recharge it on the go, giving me effectively infinite battery life for navigation purposes. I did a quick pre-race check, plugging the watch into the power bank and waited for the “charging” symbol to appear. And waited. And waited. No symbol. No recharging. No navigation. F***, sh***, b****cks. Even my mobile phone would not be much help as navigating with that drained its battery too. I would have to rely entirely on the course markers that the organisers had laid out, which I’d not done for a 100km ultra for a very long time.

So, it was with trepidation and a sense of foreboding that I lined up along with three hundred or so other runners at the start line, as we counted down to 7am and the start of the race. The town was still utterly quiet as we ran through the streets, past the outskirts and across the small hollow of flat farmland that lay around Buzet between the town itself and the surrounding hills. The first few kilometres went by quickly, as while the slope undulated, the gradients were gentle and it was on either road or good quality track, and it wasn’t long before we entered the woods that signalled the start of the first climb of the day, 600m of vertical towards the first checkpoint at Prapoce. The temperature was perfect at around 10-12 degrees, no rain, minimal wind and the path was wide enough for 2 or 3 people and generally good quality with little mud and a power-hikeable gradient. I got my poles out and was positively surprised how much my uphill speed had improved since the Winter Spine and TransGranCanaria races earlier in the year. All that incline training on the treadmill with the weight vest had clearly paid off. I had set alerts on my watch every 30 minutes to remind me to drink and every hour to remind me to eat, and this time (again learning the lessons from TGC) stuck rigidly to that plan, so that by the time we hit the short descent to CP1 at Prapoce, I had already downed a PrecisionFuel gel and was finishing off the second of my 500ml flasks, giving me 170g of carbs over 1hr40m, and I was already 20 mins ahead of my schedule to hit an overall time of 17 hours for the race. I had decided to “double-up” on carbs in my drinks, adding MountainFuel powders on top of the Naak electrolytes provided at the checkpoints, so that I could maximise my carb intake without the need to worry about chewing or digesting solid food, at least for the first half of the race, so spent only a few minutes at the checkpoint before I was on my way again, towards the next big climb and the high point of the race, Mt. Gomila (1026m).

This climb was somewhat steeper but was more open and with the limestone soil draining well it was surprisingly dry (given the recent heavy rains) and again was an enjoyable climb and one where I found myself gaining places. As we reached the flat summit plateau, the temperature dropped and the wind picked up, but it was still not cold enough warrant putting on any extra layers – I simply rolled out my compression sleeves to cover my arms and already felt warmer. The descent was really fun – at first there was a fairly well-defined path among mixed grass and rock, with the soil soft and giving without being slippery, after which it entered pine woods with a number of traverses interspersed with switchback sections, and some great views whenever the trees cleared or when the path passed over the top of cliffs or rocky outcrops. If you like fast trail running with hills and just enough technicality to make it interesting without slowing you up too much, it’s a fantastic course. By the time I arrived at CP2 Trstenik I was 35 mins ahead of my 17hr plan and felt strong and happy with how things were going. There was only one more large climb to come before the descent back to Buzet and access to our drop bags.

It was largely more of the same terrain – pine forests, limestone outcrops, single-track paths but good quality ones and soft-but-firm ground to run on – with the sole exception of a short muddy section on the climb up to Zbevnica (1014m). With it having rained a lot recently, and with the forecast for a spell of heavy rain later in the day, I had decided to wear a pair of thin waterproof socks (360Dry) but so far there had been absolutely no need for them. After passing the summit – another bare flat top with scattered limestone boulders – the long descent down to Buzet commenced, which again proved to be very runnable but with just enough rocky sections to keep the interest level high. By now, the Blue 110k route had joined up with the Red 160k (100 mile) route, so I found myself overtaking some of the athletes doing the longer course. They had started at 5pm the previous day, so had been running all night and had taken around 18 hours to cover the first 80km or so of their race. The field of the 110k race was already pretty spread out, so I was finding that I was encountering more Red than Blue runners, and half-wondered whether I might have been better to have taken on the longer Red course.

Eventually the forest paths gave way to double-track and then asphalt as the course hit the plains around Buzet and I followed a couple of other Blue runners across 2 kms of flat road back towards the town centre and CP3.

CP3 Buzet to CP6 Grožnjan

CP3 was only 42km into the race, so rather early to be accessing drop bags, but I needed a toilet break and it was a good opportunity to top up my stores of gels, as well as downing some chocolate without having to faff around with empty wrappers for the rest of the race. I managed to get all my admin done in around 20 minutes, probably a personal record for me at a CP with drop-bag access and felt refuelled and refreshed as I set off again, still 20 minutes ahead of my schedule despite the break.

The remainder of the course was essentially a straight-line dash to the coast at Umag, with a slight loop at the beginning to encompass the dam across Lake Butoniga, the site of CP4. As soon as I left Buzet, the rain that had been forecast started to fall. I had decided to go with the lightweight Inov8 Ultrashell waterproof top, as the rain was not forecast to be too heavy, so stopped by the side of the road to put it on before starting off again. The rest of the race fell neatly into two pieces – 3 sections with multiple short hills (300-500m of ascent on each) followed by descents amounting to roughly 45km in total, and 2 final sections of around 25km comprising gentle downhills or flat trails and farmland. The toughest section would be the first, as there were 3 hills to negotiate with lots of false summits.

The rain eased off, but with heavy dark clouds looming overhead I decided not to stop and remove my outer layer but to keep it on to the next checkpoint. Big mistake! While the dark clouds still loomed, the temperature rose and when the sun came out from between the clouds – which it frequently did – the sunlight was quite intense and made the climbs very heavy and slow going. I felt like I was being cooked like a lobster. It is strange how your decision-making can go awry at times like these – the obvious thing to do would have been to stop and take off my jacket, but inertia and a reluctance to divert from my intention of waiting till the next CP kept me from doing the obvious and sensible thing.

By the time I finally arrived at the Butoniga dam, I was feeling pretty dehydrated, and my last pee had been so fluorescent orange that I suspect it would have glowed in the dark. I took the opportunity to remove my outer layer, and also downed 500ml of water at the checkpoint as well, refilling my water bottles now with just the Naak electrolytes to reduce the concentration of my fluid intake in an effort to improve my hydration levels. Although I had found the last section hard work, I was still well ahead of my target timings, and had in fact gained an additional 10 minutes, so I was quite relieved as I set off for CP5 and the next set of hills.

One of the things I noticed about Croatia is how empty it seems. This is particularly apparent when you pass through rural villages and towns. Several of the villages appeared almost completely deserted, with houses boarded up, shops all closed, no cars on the road, and no people to be seen. After the race, I did some research on the population changes in Croatia since 1991 and the results were astonishing – since 1991 the overall population has fallen from 4.8m to 3.9m, almost by 25%. Contrast that with the UK, where the population has grown over the same period by almost 20%. No surprise there were so many “ghost villages”.

The next stages were pretty similar in profile – two climbs followed by easy descents. The terrain continued to be relatively easy underfoot and while the rain had eased and the sun had come out, there was a continued dark pall of clouds ahead of us on the route. The climb before the next checkpoint summited in the beautiful village of Motovun. While quiet, this was a little bit more lively than many of the deserted villages we had passed through and there was a café at the very top of the village with stupendous views of the surrounding Istrian countryside. I half-thought about stopping for a coke or ice cream, but pressed on as the next CP was only a couple of km away down the hill in Livade.

It was now 5.30pm and after another lightning-fast pitstop, with just a handful of crisps and a refill of my water flasks, I was on my way again, this time carrying my headtorch in the front pockets of my vest so that I could quickly put them on once the light began to fade. There had been continuous ominous rumbles ahead of us on the trail for over an hour, and while we were lucky enough to avoid being caught in any of the thunderstorms, the ground became somewhat muddier as we slogged up the final two climbs towards Grožnjan and CP6. The course followed what looked like an abandoned railway track, passing through a couple of disused tunnels, and as the light began to fade, I pulled into the checkpoint bang on 8pm, 40 minutes ahead of my target and with the remainder of the race now being largely downhill.

CP6 Grožnjan to Finish Umag

I raced quickly through the checkpoint, filling up my water bottles one last time – this time just with the Naak electrolytes provided for us and not adding any extra powders to them – and headed out again with just a couple of minutes to put my headtorch on. Although it was dark, the next 8km was really easy cruising along double-track and I was able to keep up a good pace. It just under an hour before the lights of Buje appeared, with a short climb up on roads through the town to reach the final checkpoint.

With less than 2 hours to go to the finish, and more than a bottle and a half of fluids still left, I went straight through the checkpoint and hit the double-track again. More rapid progress as the track turned to road, until I started to worry about the suspicious lack of red flags marking the way. For the entire race up till now I had relied on the course markings, which had in fact been outstandingly clear so far, so I was nervous that I might have somehow missed a turning in the dark. I switched on the course tracking on my watch and saw that I had indeed missed a right turn 1km back along the course. Muttering swear words under my breath, I retraced my steps and before long saw the beams of other runners’ headtorches and the row of red flags by the side of the trail that marked the turning that I had missed. That mistake had probably cost me 10-15 minutes.

The path continued to be flat or slightly downhill, but the conditions underfoot worsened as we hit the coastal plain and the farmland that surrounded Umag. The earlier thunderstorms had turned the path to a muddy mess that alternated between sticky mud that caked your shoes and made it hard to run, and slippery mud that threatened to send you skidding onto your butt. I was forced to slow to a half-jog / half-power hike, which was frustrating as my energy levels were still pretty good and I would have liked to go faster. That section seemed to take forever, but in reality it was maybe 7-8km of awkwardness, and I was still on track for a 16hr-ish finish. The lights of the main roads approaching Umag appeared on the horizon, the muddy fields gave way to track again and it wasn’t long before I was running through the familiar roads of Umag that I had driven through the day before. The course took a detour around the harbour and as I neared the finish line I could see Young Sil videoing me coming through. I crossed the line in 16h05m, almost an hour ahead of my 17 hour target and a time I was really happy with, particularly as the race had felt quite comfortable throughout and I’d had no real problems with fuelling, chafing, tendonitis or any of the other problems that have affected me in the past. It really did feel as though I had left a fair bit in the tank while still delivering a decent performance.


One of the great things about many ultra trail races is that they take place in beautiful locations, and ones that you might not ordinarily visit. We spent the remainder of the week visiting some beautiful parts of Croatia – a couple of days in the Plitvice Lakes National Park, where the waterfalls are truly spectacular and well worth a visit, and another couple of days in Krka National Park, with some beautiful limestone / travertine canyons, caves and yet more waterfalls (and some fantastic seafood restaurants). We finished with spending the morning before our return flight in the Adriatic port of Sibenik, which has an interesting history as well as a well-preserved cathedral and three striking hilltop castles.

A month has passed now since the race. I’m still buzzing a little bit from having a race that just went according to plan on almost every level. Fuelling went well, hydration went well, no chafing issues, and fatigue both during and after the race was better than expected. The course itself is very scenic, and very runnable, while at the same time having enough climbing and semi-technical sections to be interesting – it’s certainly a much easier course than was GranCanaria, and an order of magnitude easier than Ultra Trail Snowdonia (my next race) but as a fun race in its own right, and as preparation for longer / more challenging races, I’d highly recommend giving it a go, particularly if combined with a longer holiday to experience the rest that Croatia has to offer.


Pack: Salomon Adv Skin 12 + Salomon Pulse belt

Shoes: Inov8 Roclite Ultra G320

Waterproofs: Inov8 Ultrashell (Top), Inov8 Ultrashell (Bottom)

Socks: Waterproof: 360Dry

Shorts: 2XU compression shorts

Top: UnderArmor sleeveless compression top, Shinymod UV sleeves, Montane Dart ZipNeck (back-up)

Underwear: JustWears boxer shorts

Gloves: Montane VIA Trail Gloves

Hat / Buff: SealSkinz waterproof cap, 2 buffs, plus 2 spare

GPS: Garmin Forerunner 945

Headtorch: LEDLenser Neo 10

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