Eradicator/Biolab Conduit (BBonus)

This level is a big morass of smallish rooms interconnected in a fairly convoluted manner. They're mainly in two adjacent groups, which are connected by teleporters and ducts. The main objective is to find and destroy three power conduits, which will enable the exit door.

First half
When you enter the level, look behind you. There's a secret area behind that display panel on the wall. Whenever you see one of these panels, look for a secret area inside. There are two more like it within the level. Go to the next room, where there are two bio-chambers, one of them broken. Another display-panel secret area is to the right. Continue to the third room. Up on the wall to the left is a doorway overlooking a side room. In there, look on the floor for a section with the texture at half-scale. This is a hidden lift to a secret area.

Back in the room before the side room, continue to the last room in the series, which has a glass cage in the middle. There are two ways to go from here. If you like, take the left-hand way and clear out enemies up to where you come to a teleporter. Avoid the teleporter for now, unless you got the Invulnerable in the glass cage and it hasn't run out. It leads to the middle of one of the nastiest traps in the game. If you do have some Invulnerable left, take a look and you'll see. The teleporter in this "Traps Room" goes back to where you came. If you don't want to tempt fate, skip it for now; you'll come to here later.

Second half
In the room with the glass cage, go to the room that was to the right when you first came in here, and destroy the power conduit. Look on the floor for a patch that's brighter than the rest. This is a hidden lift to a network of ducts connecting the two groups of rooms. Explore the ducts, and you'll find two more lifts. (There are lots of items down here too.) Go up either of the two lifts: each goes to a room with a power conduit. These two rooms are connected by a third room. Destroy the conduits in both rooms to complete the rest of your main objective and enable the exit door. In the room with the closing door, jump up into the passage where the conduit was. To your right is another hidden power conduit down a narrow passage; destroy this one too. This enables a second door in the room with the level exit that has a secret area.

Back in the room between the two conduit rooms is another display-panel secret area behind the glass. The large door goes to the Traps Room. When you open the door, stop before entering if you haven't been in here yet. You'll see what this famous trap is. If you had teleported into here from the other group of rooms, you would be right in the middle of all this. It would have been possible, but difficult, to avoid the mines, but more likely they would have gone off and you would have taken a ton of damage. Coming here through the door instead, you can destroy them from outside. (It's unclear what those mine-enemies are properly called. They're referred to as "MiniStay" in the level editor, but that doesn't say much.) The far door goes to the final room with the level exit, but first take the teleporter back to the other group of rooms. Turn around after teleporting: you'll be back in front of the teleporter that goes to the Traps Room, but now a secret area has opened next to the teleporter.

Exit and bonus
After destroying the conduits, go to the final room past the Traps Room. Inside the door at the far end (three doors in series, actually) is the level exit. To the right up on the wall is the secret area and door with the magnetic lock that the hidden conduit unlocked. Before leaving, stock up on ammo and items, as the next level is quite severe and difficult. When you're finished, take the exit to the final part of your mission.