holding cells are an underground storage facility for those villains that the
X-Men deem too unsafe to let roam about freely. The holding cells consist of
small titanium-steel cells with the same type of door. Various safety measures
can be taken such as erecting an internal force field to back up the
titanium-steel walls, a nullification field to 'switch off' mutant abilities,
and various other precautions. There are also stasis tubes which hold
inhabitants in a state of suspended animation until they are awakened.