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As I use to do, I have mixed two routes for a day. In this case, they are very different one to another; the ascent is a long scramble, including some low difficulty climbs, that reach the summit by a impressive 400 ms high precipice. The descent is, in contrast, a long calm walk through bucolic meadows. But none of both is an usual route… something that, in my opinion, is an added appeal.
The ascent route goes up by Las Culebras (The Snakes), a series of wavy layers that, rising vertically over a stony slope, forms the northwest ridge of the western Vallibierna’s peak, just called Tuca de (Peak of) las Culebras. When that ridge dissapears into the mountain face, the layers form a set of narrow ledges, thanks to which that impressive wall is affordable with some ease. The first ascent of this route dates back to 1928 and was performed by a french team headed by Jean Arlaud, considered the father of difficulty climb in Pyrenees. But nowadays Las Culebras is not an usual route. For years, it was quite forgotten. In guidebooks, the most recent reference I have found it's in the classical "POSETS-MALADETA" by Armengaud & Jolis, which last edition was in 1968. On the Internet, only a couple of reviews, both without many details, being memories of climbings done more than 20 years before. In my opinion, something not understandable by the beauty, affordability and adventurer character of this route.
The descent route pass by Sierra Negra (Black Range), a wide grassy divide that takes name of the colour of the ground, before going down to the village of Benasque, trough vast sloping meadows. The route is very beautiful but its length (more than four hours descending without counting stops, it would be seven to go up) made it rarely used. This long return allows to go to Benasque without the Vallibierna bus when private traffic is forbidden in the valley.
Las Culebras is not a difficult path... in the meaning that this term is used in climbing but there are some things to take in account. No matter how easy it is, 400 meters are a considerable height to be climbed. Almost the whole route pass by very exposed ground and the upper section has no escape in case of bad weather (wet grey limestone is not a good thing!). There are not clear possibilities to place belays and not always the rock is safe enough. In short, the route is not difficult but you can’t mistake; for that I only could advice this route to people who overcomes easily at least two more degrees of difficulty. If you are ready, it is a very nice and funny route that I certainly recommend.
The whole route was made for the summer, with the bus to Vallibierna working. If not, the logical descent from the summit after climbing Las Culebras is the normal route (see the route From Pla de Senarta passing Culebras in SP). To climb to Vallibierna by Sierra Negra and return is possible in a day if you start the route where the road to Ardoners crosses the Barranco (Ravine) del Obago (see the map below), accesible by car from the road to Cerler ski station.
1.- The ascent: Vía de las Culebras (Northwest Ridge)Leave Refugio de Coronas, walking down the wide Llosás trail that goes toward the pleta (grassy landing) and lakes of Llosás. From the outset, the double summit of the peaks of Vallibierna out over the pines, on top of its NW ridge. Shortly after to pass the confluence of the Barrancos (streams) de Culebras and Vallibierna, a big cairn in the right side marks the place to leave the road and go to wade the stream.
Get out of the trail and, instead of go down directly to the bank, as the cairns mark, go upriver about 100 meters, to where a few trunks facilitate to cross Barranco de Vallibierna. It is not occasional, when my first visit in 1985, it was already like this and every year the trunks are naturally renewed. Once on the other bank, look for the path, clearly drawed in the grass and marked with cairns, that leave the "official" ford. Take it and go up by a meadow between pine trees. After rounding a rocky prominence, you will enter a great landing, crossed by Barranco de Culebras, at the foot of Picos de Vallibierna and Tuqueta Arnau.
Cross the landing and go up the opposite hillside, bringing the Barranco de las Culebras waterstream to the left until crossing it near the base of the NW ridge, which is increasingly impressive. Where the stream enters the gully that rises toward Collado de (Pass of) las Culebras, soon after the confluence with the Canal de (Gully of) Vallibierna about 2,500 m above sea level, leave the footpath and head toward a gray rocky slabs, very striking among the grass, at the foot of the NW ridge of Tuca de Culebras. From there, the views are already quite extensive toward the Massif of Maladeta and Posets, that looks beyond the long green trench of Vallibierna.
Go up by the ridge, which initially is wide and slightly tilted. Shortly thereafter, 80 or 100 meters gained, you'll find the first difficulty: a limestone wall about 30 ms high, that could be climbed by its central part (III-). At the top of, you will find a wide slab, steep but solid and full of holds (I). It gradually widens and loses tilt, while the peak of Vallibierna begins to appear on the left of Tuca of Culebras.
After that rest, you will meet Las Culebras, a multicolored bundle of vertical strata that emerges from the scree. Crawl on top of it (I), with attention since the rock is not very good: sometimes, a hold can keep in your hand. The rock improves when winning height, while the valley is being already far.
About 2,800 ms of altitude, at the height of Collado de las Culebras, that is visible to the right, the ridge is melted into the mountain face. Then, climb a few meters by a vertical wall with few but good holds (III) until finding a good place to pass to the left of the edge; that is to say, to the North face of Tuca de las Culebras. You should come to a narrow and inclined ledge at the foot of a new wall, some 40 ms, not absolutely vertical, solid and full of irregularities (III-).
This section is very impressive. Although not the most difficult on the route, it is the longest climbing, holds are rounded and exposure is strong. The view down is being increasingly impressive, as can be seen in the photos below. Next there is an easier section, less pending and with the rock forming steps (I).
When arriving at a ledge, go by to the left until crossing a secondary buttress. On the other side, the wall is cut by more parallel ledges (Las Culebras again), with rocky steps between, a few meters high each one. Overcome them (I/II) until leaving the layers. The last 80 or 90 ms below the summit are a steep slab of gray limestone with few holds (III), which can be climbed diagonally to the left, traveling about 20 or 25 meters to a buttress. Continue climbing on top of which (II -) to reach the top of Tuca of Culebras.
Turn left (E) to go toward Peak of Vallibierna, which can be seen beyond Paso del Caballo (Horse Passage, so called because it is customary to cross it straddle on the rock; perhaps it should be called "Rider's Passage"). Traverse this monolithic 30 ms long ridge (II-), crawling, walking, dropped on a side or riding the rock (it's your choice) to reach the highest point of this double peak.
Below, Vallibierna, all green, runs to the west, whereas to the other side of the valley the main crest of the Maladeta Massif rises impressive, with the Mount Aneto dominating the Lake of Llosás. You can see, in the following link, a 360º interactive panoramic image. And you also have the two samples bellow (incidentally, my current user image is taken from there too).
2.- The descent: Sierra NegraOnce back in Tuca de Culebras, go southward following the cairns, climbing down an easy rocky slope with some steps (I +), up to the gap between the Tuca and the Peak of Llauset. Then, turn to the right (W) and go down across a slope of loose gravel, to Collado de las Culebras (Pass of the Snakes).
From there, the scenery changes drastically; after the wildy rocky ascent, the divide of Sierra Negra is gentle, wide and rounded; the color that gives it its name is mixed with red, gray and green, forming a serene and surprising environment. Go westward by the top of Sierra Negra. The walk can’t be more quiet by this gently ground; there is no path... nor does it lack. Even small elevations along the range can be comfortably surrounded if you will, but it’s unnecessary.
Also the views make a strong contrasts: to the right (N), the Maladetas show their most rugged and rocky face, whereas to the other side (S), a landscape of smooth green undulations is lost in the distance.
Upon arriving at the foot of the Tuca de Roques Trencades (Peak of the Truncated Stones), go off to the left (S) flank of the divide, crossing the slope of that side directly to Collado de Castanesa. In the pass, turn right and go down by the western gully, by a steep slope of loose stones, to a grass landing. There is no trail nor cairns, but the path is obvious and the ground is not too bad.
Continue down along the axis of this ravine, called Barranco del Obago (Shady Ravine), through high grass, taking as reference the forested Sierra del Cubilar. When reaching the landing of Pleta Negra (Black Landing), where several streams meet, take a footpath that, from the left (southern) bank, crosses to the other side and go down, by the most factible ground.
The trail is narrow but clear. When you see that you're near the dirt road that surrounds Sierra del Cubilar, abandon the footpath and go directly to that which, taken at the right (NW), will leave you to Ardoners. This is a grass landing where you will find and take a footpath that goes horizontally, trough big grassy slopes, to the west. In view of Cerler, this road meets a dirt road that, taken to the left (S), leads us to the village. When you reach the first houses, take the street on the right to reach the road to Benasque. Turn right (N) and, when leaving the village, search and take a road to the right, signalised and marked in yellow and white (PR 1), that will take you across the fields, to Benasque. You will arrive the town in just over half an hour, entering near the former Red Cross clinic.