From the first blood-floored area, head left and fall into the large bloody pit. After getting the yellow skull key, continue up the stairs to the river of blood where you can run across to the teleporter floating in the large blood pool. This takes you to a platform high above this area. From this ledge, you will be able to drop down onto a lower one just south of the one you stand on. The teleporter close by takes you to an otherwise unreachable ledge leading to a soul sphere.
Drop down from secret #1 and head through the opening to the right, falling into another large blood pit area. Continue into the alcove to the left and ride the lift up to the ledge. Straight ahead of here is a gargoyle-faced switch. Press it, then continue up the nearby stairwell. At the top is a teleporter to a secret area.
This level can not be played in deathmatch, because there are no deathmatch starts. This bug is not present in an alternate version of PLUTONIA.WAD found on a specific version of the id Anthology.
On older Macintosh computers (e.g. the Performa cira 1995), this map cannot be accessed at all due to the machine itself freezing as it attempts to load it. The only way the player can progress through the game is to use the idmap cheat and warp to MAP13.
It is possible to finish the map with a rocket jump combined with an Arch-vile jump. The speciality of this trick is that you will die during the performance, but you can land exactly on the exit what is enough for the accomplishment of the map.