The other passes you by a shotgun guy which will be quite a relief. Both paths to the east lead you deeper into the level, one without a weapon upgrade for some time, unless you're hot for fisting SS Troopers. The opening area is almost pitch-black with torches defining your path and Nazis and zombies on the other side of the object barriers. The crossfire in said area would probably be dangerous but Joe has given you an invul sphere. Spoiler: it's in one of the various Hitler pillars in the northwest room.

The blue key is in a similar situation but there is absolutely no marking whatsoever.

One of the chambers has an automap that reveals the location of the red key, which is hidden in a secret. The path to the north is a series of functionally identical rooms with monster cages in the center and pillars on the sides and it's pretty blah. There's a not-so-Wolf-ish staircase leading to a basement with what I assume is a swimming pool. The opening segment is okay as far as Wolfenstein 3D stuff goes.

Wolfenstein 3d soundtrack