Visitors descend on Britain's steepest passenger railway, with a gradient of 1:1.8, to make the Deep Mine tour. They travel in a specially made 24-seat car, on a track with a gauge of 3ft (0.914m).

Historically the 16 floors at Llechwedd mines are all identified in relation to the point where the slate was found in 1849, after three years of costly exploration. This became known as Floor 1, the entrance to which is now hidden behind the concrete lining inside the passenger incline, but is 49ft (15m) beneath the modern working surface.

The floors were numbered upwards (1-7), and lettered downwards (A-I), so that passengers board the vehicle on Floor 2, which is at 849ft (259m) above sea level. Alighting at Floor A, 99ft (30m) lower down, passengers eventually descend a further 32ft (9.75m), via 61 steps to Floor B, by which time they are 450ft (137m) beneath the summit of the mountain.

The tour was opened to the public in 1979 and upgraded in 1992, using new technology installed by one of the main Euro Disney contractors. It involves a 25-minute walk through ten chambers, each with a different sequence of son et lumiere presentations. It is normally heard in English but, by prior arrangement on the surface, groups may hear it in Welsh, French or German.