The Blue John Cavern in Castleton is a show cave. Stalagmite formation occurs only under certain pH conditions within the cavern. Small scale mining takes place in Treak Cliff Cavern. Josh and Frank, however, find another way out through a crevasse in the cavern. His voice seems an echo from the depth of a bottomless cavern. Mining still takes place in Blue John Cavern and Treak Cliff Cavern. Elstree also housed the Tears of Allah underwater cavern, which took three months to construct. A passage in the left of this entrance which leads to a mud cavern. A mountainside, at the magician's cavern. Elstree also housed the "Tears of Allah" underwater cavern, which took three months to construct. Jason chases Fred down the hole, which leads to a large cavern. The hunters start a forest fire that forces Anna to dig into the cavern. The MTA completed excavation of a long cavern in June 2009. Malebolge is a large, funnel-shaped cavern, itself divided into ten concentric circular trenches or ditches. Quox arrives, bursting through the main cavern.