Crushing walls

Crushing walls was an enchantment spell that turned a room surface into a death trap.

Effects
A wall, ceiling, or floor of a room could be enchanted to slowly move toward the opposite side whenever someone other than the caster entered the room. The spell remained permanently in place until triggered by a creature larger than a typical rat (3 lb/1.4 kg or 0.5 ft3/0.014 m3), whereupon the enchanted surface moved inward at a rate of 3 ft (0.9 m) per minute, eventually crushing everything in the room. The size of the wall, or portion of wall, that could be enchanted was a square whose sides were equal to twice the caster's level in feet (multiply level by 2 ft/0.61 m).

The surface continued to move, pushing all in its path toward the opposite surface unless stopped by:
 * the caster
 * one or more creatures exerted sufficient strength against the moving surface. For comparison purposes, an adult hill giant might have been able to stop the crushing wall
 * a strong wooden, stone, or metal object that could survive a crushing blow was placed between the two surfaces
 * dispel magic or similar disenchantment is used to counteract the spell

If the movement of the surface was stopped for three full minutes, either by reaching the opposite surface or being held back by force or obstruction, then the room returned to normal and the spell ended. Note that any debris in the room would probably prevent the two surfaces from actually meeting, leaving a small gap partially filled with crushed rubble.

Components
In addition to verbal and somatic components, this spell required a cube of iron and a walnut shell.