The valleys of Yerse and Aguée via Arriousec to Peyras

This route requires you to leave one vehicle at the finish (E) (Peyras, Monastère de Béthléem, in Saint Pé-de-Bigorre) whilst the other takes you to the starting point (S).
For the starting point, take the road leading from Nay to the Col du Soulor. After Arthez-d'Asson, head for the hamlet of Les Aoules.
Park near the houses in the hamlet of l'Arriou-Sec.

(S) Take the path, marked in yellow, following the course of the Arriou Sec stream upstream. The climb is gentle.

(1) At the Ravin de Castéra, refresh yourself at the spring of the same name (indicated by a sign and several markers in the trees).

(2) Pass through the Ravin du Monbula, which is more striking than the others.

(3) At the 812 m mark, fords the Arriou Sec and begins a steeper climb towards the mountain pastures.
Depending on your pace, 1½ to 2 hours after setting off, you will reach the first mountain pastures at an altitude of around 1,000 m.

(4) Head back into the woods briefly.

(5) After 15 minutes, you’ll emerge onto the large summer pasture meadows.
From there, progress may be hampered by ferns and brambles in the middle of the path.
It is the outcrop of Sainte-Suzanne marl (black schist, often yellow on the surface due to weathering) that encourages the growth of grasses particularly favoured by the herds.
Then reach the stream bed, which you cross and follow until you turn off towards the Cabane de Yerse, situated on the left-hand side.

(6) The Cabane de Yerse nestles on the heights of the valley of the same name, right in the middle of the mountain pastures at an altitude of 1,275m, dominated by the Pic d’Estibette (1,851m). It has been beautifully renovated in true mountain style, although an attic floor has been added, which does not detract from the overall appearance.
It is open all year round to hikers, cavers, photographers and herders.
After a well-deserved break of a good quarter of an hour, it’s time to get back on the road, as it’s a long way to go – this isn’t the place for a midday snack!

You have the choice of descending to the bottom of the valley or staying on the contour line to reach the Col d’Espadres, which can be seen to the east.

This unmarked route largely follows the contour line, winding through the young beech forest that stretches across a magnificent, vast sharp limestone pavement. This marks the boundary between the limestone rocks of the karst landscape and the marl of Sainte Suzanne. It is along this boundary that the most remarkable cavities (chasms, etc.) are generally found; the route passes close to several of them.

(7) 25 mins after the Cabane de Yerse, reach the Col d’Espadres.
Whether looking east towards the Aguée or west towards the Yerse, the view is magnificent and the place is steeped in mystery. Herds of horses are often found here, sometimes accompanied by donkeys.
In winter, a snowfield blocks the eastern face of the pass, hindering the descent towards the Aguée. But in summer or autumn, no problem!
So resume the route by descending the pass towards the bottom of the Aguée valley, either by passing north of the ruined Espadres hut, or south between the sinkholes, several of which have collapsed or are flooded by the numerous nearby springs.
Descend gently through the entire Aguée valley, on unmarked paths or cattle tracks, through an area with little or no woodland. Find a lovely, lush meadow to enjoy your long-awaited snack.
Then resume the path, passing close to old shepherds’ huts (ruins or traces) and reaching a large clearing at 960 m, with a meadow sloping up the southern hillside of Sarro Pourcou (Serre Pourcou), the mountainous ridge that overlooks L’Aguée to the north and ends at Cap des Litas (1,300 m) to the east.

(8) Continue eastwards until you reach the edge of the forest at a place known as ‘Cul de l’Aguée’.

(9) Of the various streams of the Aguée, one of them disappears into a small sinkhole in the middle of a large pool covering a few square metres beneath the beech forest.
A path leads off from here to the Picharrot waterfalls, but as it is difficult to follow in this direction, it is best to avoid it.
Including breaks, I arrived there 5 hours after setting off from Arriou Sec.
Head back to the large clearing you crossed shortly before.

(8) Head up to the right, through woods and bushes, climbing the nearly 300 m to Cap des Litas. Avoid getting too close to the edge of the State Forest (green line on the map), as some rocky outcrops hinder progress.

(10) Descend the opposite slope through fairly sparse woodland and head towards the bottom of the valley, known as Bat Séco or Cabane des Italiens (names not shown on the IGN map).
At the 1130m mark, in the middle of a vast beech forest, you reach the bed of the Ruisseau de la Fontaine d’Ariails (not shown on the IGN map), then the path branches off eastwards, joining the bank of the Ruisseau de la Gargante at the 969m mark.
Here, amidst the beech trees, it is the bed of a small, harmless stream, but further downstream it becomes a deep, impenetrable and treacherous ravine flowing into the Génie Longue!
Here you will find the yellow markings (wide and quite old) of the Nature Reserve and a blue marking (recent) of the Saint-Pé Integral Biological Reserve (RBI).

(11) Here you have the choice of heading back into the valley via the Tachouères (badgers) path on the right, which seems quicker in terms of time but is an infinitely long way to go, or the Aülhet path, which involves a slight climb. This particular walk opts for the latter.
So turn left, carefully following the yellow markings clearly marked on the trees.
The route passes south of Soum de l'Artigue, at a clearing with a drinking trough, at a place called Hount-Débat.

(12) You’ll reach the Cabane d’Aülhet with no trouble; it has been clad in new timber (since October 2016).
Then take the yellow-marked path (recent but very narrow) which descends from the mountain pastures to Peyras, via an ancient pastoral track, which is quite steep and very slippery in wet weather. If this is not the case, runners will be able to enjoy themselves to their heart’s content.

At the Pla dé Bers junction, at an altitude of 824 metres, leave the Tachouères path to your right and continue straight up the slope to reach the vehicle you left there in the morning or the kind soul who has come to collect you (S/E).

As is often the case, I’m taking you along little-known, unmarked paths that are sometimes rather hostile to hikers: particularly here, the edge of the Picharrot cliffs and the heights of Sarro Pourcou.
Sarro Pourcou, or Serre Pourcou, is this vast expanse of forest on the ridge (the serrat) of the mountainous hilltop stretching from the Col d’Espadres to the Cap des Litas.
All these ancient places, their shepherds and, at times, the paths are briefly described by Abbé B. Abadie in his 1969 book *Le Sanglier du Picharrot*.

Warning!
This hike takes place in the heart of the wilderness in an environment that can be challenging: steep slopes, rocky outcrops, cliffs, thorny vegetation, and at times a complete lack of markings or even a path... This is why it is reserved for experienced hikers with a good sense of direction. A GPS device may also prove very useful.
Shortly before WP (7) and up to WP (11), there is no marked path on the map. This does not mean, however, that there is no path at all...
Furthermore, the Visorando track for this hike between WP (10) and (11) remains approximate due to poor satellite reception in this area.
I have classified this hike as "Difficult" due to the difficulties described above, particularly the numerous sections off-trail and unmarked, and above all because of its length and elevation gain. It is a challenging route, suitable only for experienced hikers.
In winter, if there is snow, the rating would be upgraded to “Very difficult”.

Estimated time
I completed this route in just under 8 hours, including breaks and a picnic. This is a reasonable time, given the route’s difficulties, but also the time spent exploring around the Porto de la Gleize (below the Col d’Espadres) and the Cul de l’Aguée. So set off early and allow at least 8 hours to be on the safe side.

Water points
There are no fountains along the route known to provide drinkable water.
However, the one at Castéra is acceptable, as no livestock graze nearby.
If necessary, from June to October, you can top up with non-potable water at the Yerse hut (tap nearby) or at the Aülhet hut and boil it to make it safe to drink.
You should be wary of all other springs or water sources you come across, as drinking water in the mountains is not guaranteed to be risk-free...

Places to stop and take shelter
In the event of heavy rain or storms, the two mountain huts (6) and (12) are the only places offering proper shelter along the route. There are also a few makeshift shelters made of low walls or rock faces dotted here and there.

Equipment
Bring standard equipment for mid-mountain hiking (hiking boots, suitable clothing, rainwear, water, food, survival blanket, knife, compass, map, whistle, GPS...).

Traffic
In spring and summer, from waypoints (S) to (7), then (12) to (E), you may encounter a few hikers, cavers, shepherds or the occasional livestock farmer. Very rarely anyone in winter.
Elsewhere, the route is completely solitary, summer and winter alike, except for herds of cattle, sheep and horses from June to November.

Spelling of place names
Several place names have different spellings: in Occitan, Bigourdan, Gascon, Frenchified Gascon, French, distorted IGN, ...

Flora and fauna
The vegetation of this mountain range reflects the severity of soil drought caused by the terrain and the nature of the substrates
, but this is offset by very high rainfall and cloud cover: boxwood, beech, lime and hazel are ubiquitous… This is why the wooded slopes are very damp and sometimes very slippery. (source: Saint-Pé Tourist Office).
Part of the hike, between waypoints (9) and (11), takes place within the Saint-Pé “Integral Biological Reserve”, covering 1,010 ha of the 2,588 ha of the undivided forest of Saint-Pé (see the ONF.fr 1 and Natura 2000 websites).
On the subject of why “dead” trees are left in place, there are some interesting articles on the Wikipedia pages on Deadwood and List of ancient primeval forests.

With a bit of luck, you may also come across a wealth of wildlife. In particular, wild boar, roe deer, chamois, occasionally mouflon, countless birds and various insects, and sometimes amphibians (frogs, toads, newts).

Variations
You can enhance this route by:
- a short detour via the Porto de la Gleize (and its nearby chasm), to the north between Espadres and the Source d’Arials,
- a continuation beyond the Cul de l'Aguée, for experienced hikers or climbers, with great caution, to admire from above the vertiginous cliffs of the Picharrot and the deep ravines, carved by ancient waters and perhaps still by the fury of modern storms,
- a visit to several caves, chasms and karstic caves, most of which are not marked on the IGN map (1,600 cavities are recorded in the massif), provided you have the skills and equipment!

A bit of history
The forest of Saint Pé is also known as the forest of Très-Croutz (or Très-Crouts or Tres Croutz or Tres Crouts or Tres Crots).
The origin of the name “Très-Croutz” is thought to derive from the “Trois Croix” (very croutz in Bigourdan/Gascon) carved into the stone at a place called “la Toue”, right in the heart of the massif, at an altitude of around 1,400 metres.
The Three Crosses bear witness to ancient pastoral conflicts between Asson, Salles and Saint-Pé-de-Bigorre.
In 1569, the Bearnese Protestants of the Asson valley decided to attack the Bigourdans of the Estrèms de Salles, with whom they were disputing the Azun and Maumula mountains. The 1,500 men intended to lay waste to the village of Salles and seize all the livestock from Vergoun. But the battle was won by the Bigourdans. These conflicts became so serious that the King’s army had to be called in. It was impossible for the Bishop of Tarbes to restore harmony. Source: Abbé B. Abadie, *Le Sanglier du Picharrot*, published by Marrimpoey Jeune.
At a place known as "Très-Croutz", the bishoprics of Tarbes, Lescar and Oloron converged on this mountain.
Today, all that remains are three crosses carved into a rock and the inscription 1716. They can be found on the IGN map between the "u" and the "e" of "La Toue".

Nearby attractions
- The town of Lourdes, the Marian Shrine;
- The Batsurguère valley;
- The village of Saint-Pé-de-Bigorre, the village itself, its cultural heritage, its events, the remaining part of the Très-Croutz forest and the trails in the Pibeste-Aoulhet Regional Nature Reserve, water sports;
- The story behind the reserve’s new signposting in autumn 2014;
- A little further on, the Gaves Valley

Find out more...
- It is worth consulting the website and publications of the Pibeste-Aoulhet Regional Nature Reserve. The most notable is the "reserve guidebook", packed with information, routes and anecdotes!
- The Saint-Pé Tourist Office also publishes numerous brochures and detailed hiking suggestions. One of the brochures may be of interest for discovering the massif’s flora and fauna: the Karst Trail Brochure, even though it does not cover this particular hike.
- The former Ferme de Peyras, now the Monastery of Bethlehem.
- You can immerse yourself in local literature:
Abbé B. Abadie, *Le Sanglier du Picharrot* (published by Marrimpoey Jeune),
Jacques-Emile Mengelle, Bigorre de mon enfance,
Jean-Claude Mengelle, Le solitaire de la Gargante.