Sewer3

The ruins of the sewer system from the previous map, and the connecting tunnel to another poorly-maintained sewer overrun with mushrooms. This is the shortest map in the game, and contains only a single puzzle.

Past events
Alex Hartman attempted to track down Jeff Walter in his maniac desire for revenge. Hartman assumed Mikhail Rosenthal would assist to find Walter. The search didn't seem to go anywhere, and Hartman began to doubt Rosenthal would be of any real help. However, Hartman somehow found out Rosenthal was keeping tabs and informing Walter of his plans. Hartman felt that he had no choice but to kidnap Rosenthal, and imprisoned him in his hideout. He kept Mikhail Rosenthal inside of a small cell at the bottom of the sewers, where he murdered Rosenthal, and presumably disposed of the body.

INFRA
When Mark regains consciousness, he finds the control room's floor gave way, and made a previously blocked-off doorway accessible. He crosses over a broken sluice gate to look for an exit.

Extended Sewer
The extended sewer is the label given to the stretch of sewer under the control room of the previous map. It is in horrible condition, the waterways clogged with sludge and litter, glass windows in the control room broken, concrete crumbling, and masses of glowing green mushrooms growing in the sludge below. The air near the floor is visibly noxious with mushroom spores and gases.

Hartman's Dungeon
Alex Hartman's dungeon was a simple set up. A small cell behind chain fences comprised the living quarters. The cell was furnished with an old, stained, mattress, a bucket, a chair, and chains. The outside of the cell is populated with tools (screwdriver, pliers, hammer), dynamite, and a tape recording with Hartman's confession. It is inferred that this room was used to hold and torture Rosenthal for information on Walter's whereabouts.