This level occupies the map slot MAP31. For other maps which occupy this slot, see Category:MAP31.
Secret Exit: During the map progress, the platform behind the rocket launcher east of the lift you rode down from the map start will lower. Use the teleporter and carefully ascend the stairs in front of you as stepping on every second stair opens the pair of gargoyle faced stone walls behind you, releasing monsters. Walking between the topmost candles (on the second stair from above) for the first time (note: do this before using the switch in the monster alcove) lowers a wall in front of you, preventing you from using the gargoyle switch behind it. (Actually it is possible reaching the switch by straferunning over the trigger so that the wall lowers behind you. You can open it from inside.) Descend some stairs and open the lights in the back wall of the third eastern monster alcove, revealing a switch. Push it (note: you can do this only once, so do not push it when the wall has not been lowered yet) to open the wall upstairs and use the gargoyle switch behind it to lower the southernmost walls, revealing a megasphere and a new teleporter that leads to a white teleporter (sector 362) near the secret exit to map MAP32: Have @ It. You can explore the rest of the map and decide later to use the normal or the secret exit.
Stepping on the topmost stair (see official secret #1) opens a door downstairs. Enter it and push the switch to open the western door. Enter the teleporter behind it to land up in the first room you entered in this map. Walk to the northwestern part of the map and kill the cyberdemon. There is a niche with a fake switch in the northern wall of the room he was hiding in. As you enter the niche, a wall in the south starts rising. Quickly (strafe)run there and step on it before it is risen to high. After the wall stopped rising, walk to the east on the ledge and use the teleporter to get to a secret place (sector 392). There you find five rocket boxes, five bulk cells, two soul spheres and two megaspheres. Since you will not be able to come back here without cheating, grab anything you can. Step on the demon face on the floor to be teleported back to the first room you entered in this map.
It is possible to get stuck in the room where you encounter the first cyberdemon: You open the door to this room from outside (Linedef 242, Action 117: DR Door Open Wait Close (fast)), cross the trigger to close the door (Linedef 54, Action 110: W1 Door Close (fast)) and have to reopen it by pushing a switch (Linedef 106 Action 112: S1 Door Open Stay (fast)) that can only be once used. Outside again, if you press the use key in front of the door, the door lowers after some seconds and will stay shut for good, keeping you trapped inside: Either right now if you reentered the room before the door shut down or during later map progress when you will be teleported back into the room again.
There are two ways to prevent the player from reaching the secret exit/official secret #1: Either by first using a switch (Linedef 1530 Action 103: S1 Door Open Stay) to rise a wall before it is lowered, and then lowering the wall by walking (not successfully straferunning) over the trigger (Linedef 750, Action 110: W1 Door Close (fast)), thus blocking a needed switch (Linedef 727 Action 23: S1 Floor Lower to Lowest Floor) permanently. Or, similar to the previous bug, by reaching the needed switch (after using Linedef 1530), but instead of using it, turning around and "raise" temporarily (Linedef 242, Action 117: DR Door Open Wait Close (fast)) the already permanently raised wall, going to the south of the wall and waiting to let it be shut for good.
The deathmatch arena has its own secret exit similar to the one in official secret #1, but once teleported there one cannot turn back since the teleporter's (Linedefs 2808, 2809 and 2811, each with Action 97 WR Teleport) corresponding sector (420, Tag 52) is missing a teleport destination. The whole area surrounding the secret exit has a type 7 damaging floor.