Final Doom - Knee-Deep in the Dead - Phobos Lab (E1M8) - All secrets

There is only 1 secret in the final level of Knee-Deep in the Dead and it's before the boss. I still finished the game, however, since the lowering of the walls in the boss area is only triggered by killing the bosses (the two Barons of Hell) and these "all secret locations" runs are done without monsters, I used IDCLIP to get to the end of the level.

This is played in GZDoom, but I only take routes that don't require jumping (even though I sometimes jump to speed up the walkthrough).