Eben Muse had low hopes for his spring trip to Fontainebleau, thanks to a troublesome finger injury. So while his friends got excited for their bouldering projects, he looked to his trusty fallback — the trail — for salvation. And what he found was unlike any other route he'd experienced...

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Like many climbers approaching middle age, I started to suffer a slew of mostly minor but deeply inconvenient injuries which seem to allow me to fully pursue only one of my two main activities at the same time; climbing, or trail running. If it's not my sore elbows keeping me off the rock, it's my screaming shins keeping me off the trail. If it's not my tissue-paper pulleys warding me away from the moonboard, it's my IT band syndrome barring me from hill sprints. I swing hither and thither like a pendulum, achieving little of note at either, but both take turns at keeping me sane.

I had low aspirations for my spring trip to Fontainebleau this year, as I had a troublesome lump in my finger which refused to respond to physio exercises. While friends got excited for their projects, I looked to my trusty fallback — the trail — for salvation. From the doorstep of our accommodation in Le Vaudoué on the edge of the Trois Pignons (Three Gables) forest, I noticed that AllTrails, Strava, and others agreed that the most attractive local prospect was some variation or snippet of something called the '25 Bosses'.

it feels unlike almost any other trail I've ever encountered

According to online translators, 'bosses' here refers to hills, however I was informed by a french friend that this is not quite accurate. A 'bosse' is in fact a hump - think 'the Humpback of Notre Dame', rather than a hill per say, or a mountain. None of them are big, but by god do they keep on coming, and together they form the undulating canvas on which a group of French Alpinists –  'la bande à Puck' (Puck's gang) – painted (in red) the 25 Bosses. It's undoubtedly one of the best and most unique trail circuits you'll ever experience, a real exercise in balance, mobility, and technique, especially if you try to go fast (which is very optional).

The Route

The 25 Bosses was pioneered by a group of French Alpinists led by Pierre Nédélec in the late 1960s, with the aim of covering as much elevation as possible, in the lowest distance. This all as preparation for the greater challenges of more conventional alpine objectives. As a resident of flat-as-a-pancake Cardiff, my hill training takes the form of trudging up and down Penarth hill, covering 30m with each loop.

you're constantly pushing, pulling, rubbing against, sliding down and shimmying up this tactile landscape

This is no such torture: Puck and his crew achieved 800-900m of ascent via a magnificent tour of the Trois Pignons woodland. The route has been slightly adjusted over the years, with the addition of  Rocher Cailleau and  J.A. Martin crags increasing the elevation and distance slightly. The trail is monitored and marked by the Association of the Friends of the Fontainebleau Forest.

In substance, it feels unlike almost any other trail I've ever encountered. This is thanks to the constant change in surface, in angle, in texture, in friction, from pushing through sandy trails and up steep rocky staircases, to using your whole body to climb past polished root terraces; bounding over boulders, ducking and weaving through switchbacks which take you through angled corridors and rock bridges and tunnels. What starts as an exercise in acrobatics and agility slowly transforms into a test of efficiency - in how to conserve momentum while following the meandering trajectory. The going is as beautiful as it is varied, and to find yourself atop a boss (it's pointless to try and keep count) peering through the canopy at the glory of this rich and ancient woodland is quite a different feeling to topping out a boulder problem in the crags below.

As for crags, you'll pass by lots of them, probably including some you've never seen before. My time on the course was extended by various side missions to peep around less-visited crags such as  Justice de Chambergeot,  Pignon Poteau,  Gros Sablons, or  Grande Montagne. As well as these, there are many spectacular lone boulders in the woods, with incredible-looking problems on them, looking great without much of the wear and chalk stains which ages other well-travelled boulders here. Though the 25 Bosses is a well-used path with its worn trails and gloss-polished tree roots, it's a way to open your eyes to crags or boulders you'd never have come near before.

You'll taste all the different flavours of Bleau - from rows of towering Scots pines and oaks, to bright silver birches, beachy sand clearings, and even stretches of open moorland and bog. It's a grand tour of this part of Fontainebleau and an exercise in getting intimate with the place, with the roughness of the course meaning that you're constantly pushing, pulling, rubbing against, sliding down and shimmying up this tactile landscape.

For someone like me who made an annual pilgrimage to this place for many years, first as a student falling in love with climbing for the first time, then as an experienced climber trying to climb as hard as I could, and then as simply a person trying to unwind and make the most of my holiday against a creaking body, the 25 Bosses represent a different way of experiencing this place, which holds so much emotional significance for climbers. What started as an exploration for a decent rest day activity ended as the genuine highlight of my trip, one I kept returning to, and will return to again.

while only 16km, it feels significantly more serious and arduous than a similar distance on an ordinary trail

Logistics and finding your way

The trail is generally impeccably marked - there are small incisions painted red on trees, stumps, rocks, at a frequency that seems at first to be excessive. However, once you've started gathering a head of steam, you'll find that the granularity of the route-finding here, with switchbacks, hairpin bends, and sudden sidesteps common, means this ever-present topo-line starts to feel fairly necessary.

Beware though - the ever-present markers appear every few meters on many sections, but they are only really visible from the path itself. If you stray even a few meters away from the course, you will struggle to spot any markers whatsoever, and will likely need to retrace your steps to return to the trail.

They are generally simple to follow. A flat line means 'you're going the right way', a bend in the line directs you to change your trajectory in the same way, a double bend means 'hairpin bend', and a red ❌ means pretty much what you would think (turn back). A dotted line forking out means there is an alternate route or shortcut available - some of the more challenging sections featuring more difficult climbs, slippery rocks, or tight squeezes, can be bypassed while still staying on the course proper. Apart from the official 'dotted line' shortcuts, there are many other possible shortenings available; the Trois Pignons forest is crisscrossed with intersecting paths of excellent quality, and many people choose to join the 25 Bosses for just a part of their journey.

I started my route at Parking de la Mée, also the car park for several smaller crags such as  Rocher Guichot,  Le Diplodocus, and  Grande Montagne, but you can start it in any of the numerous car parks on the edge of the forest, from  La Roche aux Sabots to  Gorge aux Châts. Many choose to start from Noisy-sur-École. But there's no material difference; that's the beauty of a loop!

One final consideration; hunting still takes place in this part of Fontainebleau on Mondays between September and March. Walkers, riders, hunters, climbers, all share the space, and you are encouraged to be vigilant (current info here).

A note on technical difficulty

The full 25 Bosses circuit, while technically only 16km of distance, feels like a significantly more serious and arduous undertaking than a similar distance on road or ordinary trail. It should be approached with a healthy dose of respect. Tripping and ankle-rolling hazards are constant in the form of roots, rocks, steps, and everything is much more slippery after rain. Assess conditions, be honest with yourself about your ability, and pack appropriate equipment and provisions. Some parts of the circuit involve jumping from one rock face to the next, or sliding into rock crevices. All of these can be safely avoided by going around.

What to bring

Food: The fastest unsupported time on the loop is around 1 hours and 34 minutes. You will probably be slower, and may need to bring snacks along. Don't get caught hungry, bring some croissants and enjoy yourself.

Hydration: Whatever the time of year, bring more than you think you need. 16km may sound like child's play for some, but the physicality of the terrain means you'll find it more taxing. On my first attempt I was well short and regretted it.

Footwear: There isn't much resembling 'climbing' on the trail, however there is a constant threat of slipping, tripping, rolled ankles, and bad landings. Wear something which supports your ankles in the way that you're comfortable with - many people walk the course in hiking boots, but trail running shoes are more than grippy enough, especially in dry conditions. If you hate getting sand in your shoes, like me, you might consider bringing gaiters.

Clothing: It can be hard going, so I'd recommend bringing a smart layering system, so that you can adjust for the conditions. Pay attention to the weather forecast and bring waterproofs accordingly.

Navigation: It's not a bad idea to have a system of navigation of some sort to back up the trail markers. A phone is a must, as a back up alone, but I used a GPX file on my watch to navigate, which helped me correct my course on the half-a-dozen occasions I managed to stray from the path. I did, however, get the feeling after a while that the distraction of my watch was at times the cause of my missing the markers! Physical maps of the area are available in local shops and would help you adapt the course to your needs.

Things to look out for:

Aside from the magnificent boulders I've already mentioned, there are some amazing habitats that you'll be running through, and incredible creatures you might encounter along the way. You'll travel through birch, pine, or oak woodland, you might encounter any number of different fungi (over 3,000 species can be found there), and you'll likely be moving to the soundtrack of birds which include woodpeckers, owls, warblers, wrens, and many more.  If you're hopeless at recognising birdsong like me, check out the ingenious Merlin ID app (which works offline).

As well as several panoramic view points such as  Mont Pivot and  Rocher Guichot, there is significant archaeological interest within the Trois Pignon woods, including a number of mesolithic and neolithic engravings on boulders, as well as notably strange areas such as  Le Cul de Chien. Often there is something strange and interesting around the corner, a rock shelter or small canyon. There are also a number of mysterious chalice symbols carved into the rock around the Trois Pignons. How many can you spot?

Expected time to complete the circuit:

For hikers, it's expected that the journey will take between 5 and 7 hours, with a steady pace. For trail runners, a good time would be 2.5-3 hours, while those pausing to enjoy the view more often might take four hours or more. The record as far as I can tell, is 1 hour and 33 minutes (47 seconds). Beat that!

Guidebook:

As I was researching the 25 Bosses route, I absorbed all of the information I could online, but on my daily trip to one of the many excellent bakeries at Milly-La-Foret, I stopped by the local bookstore, wondering if maybe they had some nice prints or postcards. What I found was 'En Forêt de Fontainebleau, 25 Bosses D'Enchantement' a bilingual photographic guide to the 25 Bosses trail, published by local actress and Boss-enthusiast Valérie Baurens (who was kind enough to share some of her photos with me for this article).

Not challenged enough? 35 bosses - or the Sentier des Belvédères

25 bosses sound too easy for you? I've got good news! You can increase it by 10km and a few hundred metres of height gain. Adding in a section called the Sentier des Belvédères is known as the 35 Bosses, since it adds ~10 additional bosses.

It takes you out of the pine woodland of the 25 Bosses ordinary, and into more deciduous terrain, through sparser moorland plateaus, which have a distinctly different feel to the rest of the circuit, especially in winter or early spring, as the trees let in a lot more sunlight. It can easily be looped in, as both trails meet briefly at  Pignon Poteau. It takes in plenty of rocky ground, but is somewhat less challenging than the 25 bosses proper, and feels like something of a break for the ankles.

Useful phrases to equip yourself with:

1) Good day!/Bonjour! (Bonsoir after ~6pm)

2) Hi - I seem to have lost the trail, do you see red markings anywhere? / Bonjour, j'ai perdu mon chemin. Avez-vous vu des balises rouges sur le vôtre?

3) After you! (for example, when there is a tight squeeze and no room to pass) / Après vous!

4) Any spare water for a desperate hiker? / Avez-vous un peu d'eau dans votre escarcelle pour un randonneur désespéré?

GPX files:

•  25 Bosses
•  35 Bosses
•  Sentier des Belvédères