There are no secret or hidden levels in PSX Final Doom; and
subsequently there are no "secret" exits, per se.

Level 23 ("BALLISTYX") has 2 exits, one that is accessible
in Single-player and Cooperative games, the other exit (just
outside of a caged area which overlooks a walled-in field of
short pillars) is accessible only in Deathmatch games...
What you're seeing is the Deathmatch exit.
(In Deathmatch games, only this outside part of the map is
accessible.)

Both exits lead to level 24, HECK.

--Led

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