Tok'ra tunnel

Crystal tunnels are tunnels by which the Tok'ra conceal themselves underground. When Tok'ra arrive at a new base, they immediately move beneath the surface, forming tunnels with special crystals. For the time the tunnels are formed, no life support is needed, as oxygen is produced as a byproduct of the construction&mdash;if the crystals are used with the proper types of stone.

Different sizes and shapes of crystals produce different stretches of tunnel&mdash;some long and straight, some leading upward or downward, some opening up rooms.

The tunnels are also capable of deconstructing themselves by command. The deconstruction process is particularly hazardous.