Gritstone outcrops at Stanage Edge and The Roaches, are recognised as some of the finest rock climbing sites in the world. Limestone is more unstable but provides many testing climbs. Thor's Cave was explored in the early 1950s by Joe Brown and others. Eleven limestone routes there are listed by the BMC, ranging in grade from Very Severe to E7, and several more have been claimed since the guidebook's publication; a few routes are bolted.