[9-9] E1M8: Ziggurat Vertigo

At the start, grab the Pentagram of Protection. Dive into the lava near the bridge and swim beneath it, away from the ziggurat. You will emerge in a small room containing a Quad Damage powerup, health, and a slipgate that leads back to the bridge in front of the ziggurat.

Behind the silver key door, there is a passage forward and to the left, and another to the right. Take the left passage and follow it to the end. On your right, you should see a section of wall with a dark border. Shoot this section to open a door leading to two boxes of nails.