 The tunnel is about 75 metres long and about 3 metres wide, but the ceiling in certain sections is only 1.70 metres high and at one point just 1.40 metres, so walkers need a torch and the use of a helmet is recommended.People carrying a large rucksack may find it a bit of a squeeze.Entering the tunnel at the French end necessitates climbing down some fallen rocks to reach the floor of the tunnel.