Inaccessible rooms/areas on PSX Final Doom level 18, Nukage
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There are many small hidden chambers on this level.  Some
of these are accessible to a player, some are not; but all
of them appear on your Automap if you find the Computer Map
item on this level (or if you use the Automap cheat code).

Note that none of the inaccessible areas contain monsters
or useful items, and none of them are counted in a player's
secrets-found score.

In the northern-most room on this level, there are a pair
of large, round, metallic structures near the level's exit.
The eastern-most chamber is hollow, and is used as one of
several player start points for Deathmatch games.  A player
who appears there can open a door in its west wall to exit.
(If you use the "object indicators" Automap cheat code, you
may notice an object marker inside that round chamber; but
that "object" is just a small blood stain on its floor.)