The south end of the room has a secret door leading to a small room (#1) with various goodies. In ultra-violence mode, you'll get invulnerability a soul sphere, and a rocket launcher; otherwise, you'll have to be content with a few medikits. To the east of this room is a secret door (#2) which leads to another secret room (#3) with an invulnerability sphere. I wasn't able to get credit for either #2 or #3; #2 is too small, and #3's floor is too high for me to enter.
Hit the switch on the north side of the room, then go east and then south to a small room (#4) with blue armor, health, and ammo. There are two switches in here which simply open the two yellow doors.
1 262 < 100000,fa2c0000> ( 16, -1492) 2 263 < 440000,fa400000> ( 68, -1472) 3 264 < 640000,fa400000> ( 100, -1472) 4 250 < 1c00000,fbb80000> ( 448, -1096)