Avenc 4 de les Planes del Forn del Vidre

The pit has three openings to the outside; the most obvious is the upper one. At the base of the small shaft an ascending ramp follows that connects through a narrow passage with the upper mouth. Continuing down over some uncomfortable blocks, one reaches the lower mouth. Shortly before, the cavity gains depth through a stony ramp that ends at a narrow and elongated drop of -6 metres. The gallery becomes impassable on one side. On the other side we soon reach a gaping passage; by skirting it one reaches an earthy chamber with a drop of -6 metres where the exploration ends.

It is easier to enter through the middle mouth after installing a 5 metre small shaft.

The gallery becomes impassable on one side, which is where the icy air current emerges that gives one of the names of the pit.