The Trapper Dimension consists of five islands of bare rock floating in an endless void. The first island simply has a portal, cycling through the four Alignment colours. Any of the three Ancient's colours will take the character to one of the other islands, where they will find a regenerating panel of that colour; the green portal leads to an island containing a green panel, which regenerates the Sanity of any character that stands on it, and so on. The purple portals lead to the exit island, where a dais will teleport them back to the real world.
Interestingly, at several points throughout the game, objects must be teleported using summoned trappers to solve puzzles; these objects can be seen on the exit dais by any character who goes to the trapper dimension thereafter. Among the objects is the corpse of a man, which doesn't seem to be putrefying. The bare rocks and columns themselves may be parts of the real world teleported in the ancient past.
If a player chooses the wrong portal path, they are routed to one of the three islands with regeneration panels and a portal to the exit.