Yesterday, a team of 4 went into sector 26 and had a run in with some cyberdemons. The reports that I received indicates that a few wildly placed rockets from one of the cyberdemon lords blew away a massive amount of wall structure revealing what may be an underground base of some sort. After me and a few others suited up, we locked on the coordinates of the base and went in...
The entrance to the blown out wall is pretty high in radioactivity. The good news is; there isn't very much of it at all. Looks like most of it has dried up over the days. It was pretty well guarded by a team of former human sargents, [sic] and a few "pinkos" were placed down a hall for a surprise attack from behind.
There also appears to be some sort of holding cell here for other demons. There must be a way in there, because a few items are visible.
Deeper inside the metal encased operational facility is a red key, which is important to acquire if you ever want to leave this sector. If things start heatin' up, the sargents will move this key to another area.
There is a teleporter revealed after you get the key which will take you back to the upper level of the base. But getting to it may deliver a slight problem; death.
On the way to the exit, there will be many creatures that will do their best to stop you from getting out. The exit is trapped, so watch it.
When you lower the plasma gun beyond the blue bars for access, you will notice a switch in the south. Flip it and steel bars will open in the north. Jump from the northern window and over these bars to find (on medium and hard skills a sergeant, a megasphere and) a box of bullets (sector 156). Walk toward the bars again to exit.
Exit secret #1 and go straight east, through the hall made of great bricks and the cave in its southeast. Cross the nukage pit and proceed to the tech-like looking hallway's east, where a compartment with a chaingunner on easy and medium skills or a mancubus on hard skills, also a BFG9000 opens in front of you. The southern wall's central recess has a hole in it revealing a switch and a health bonus. Shoot the switch to unveil another switch in the compartment. Flip it and four of the lights next to the walls central recesses will lower, releasing out a demon (on easy skills) or (two on medium or four on hard skills) hell knights from the north, but also enabling access to the demons' cage (sector 122) in the west, where you can find a cache of supplies: five (on easy) or one (on medium) medikits, five health bonuses on hard skills, four (eight on easy) bullet boxes, two (four on easy) shell boxes, two (four on easy) rocket boxes and four (eight on easy) energy cells.
In the large, cross-shaped hallway south of the ovoid room where you found a rocket launcher, enter the southern hall and then backtrack to the room north of the ovoid one to find that the western, blue wall has opened to reveal three (easy) or four (medium) imps or, on hard skills only, a sergeant and two arachnotrons, also a medikit on easy/medium or a health bonus on hard and a switch. Flip the switch and head back to the compartment in the north to find a corridor (sector 387) with two boxes of rockets and a backpack.
After the red key door, you can climb a stairway into the western side of the central building. There, you can drop off the northwestern window onto a tiny ledge in front of it. From there, walk to the western platform to find a compartment (sector 149) with a soul sphere.
After crossing the U-shaped wooden bridge over a large brown mud lake to the very north of the map, behind the wall in front of you go southwards to find a stairway leading up to a rocket launcher. At the south of this stairway is a portion of wall with grime on it. Open it to find an invulnerability (sector 360).
In the room opened when you try to open the exit door, the southernmost portion of the eastern wall is covered in grime. It can be opened to collect a megasphere (sector 340).
Sector 432 is marked as a secret, but is not used in the map, rendering it unobtainable.
After using the first switch in this map, some large brick walls surrounding this room lower, revealing computer consoles and an alcove with an imp, guarding the switch that opens the next door. A part of the southern computer console has hazard stripes on it, open it to reveal a super shotgun. Grabbing it lets another one appear right behind the next door.
Sector 111, the gravel sector north of the toxic pool sector in the east of the map, is also a type 7 damaging floor, even though there is no slime on it.
Due to an unused sector marked as a secret, you can only obtain 85% secrets on this level.