A short tunnel driven through a ridge of the Cordillera de la Sal in the 1930s, when the only road north from San Pedro went up the Catarpe valley rather than around it. It is unlit, unlined and cut straight into the salt-and-clay rock, with the pick marks still visible on the walls, and it emerges onto a cornice with the whole valley below and Licancabur filling the skyline.
There is not much to it beyond that — it is a hole in a hill — but it is a good target for a bike ride and it makes sense of how isolated this town was before the paved road. The Inca road to Catarpe ran through the same gap, and the Spanish used the valley as their route to the silver at Potosí.
Ride out via the Garganta del Diablo and come back along the river, about 20 kilometres round trip on dirt. Bring a light if you want to look at the tunnel walls properly.