Exploding Wall - from The QuakeLab or Exploding Walls v1.0 from The QuakeLab is a Single Player level.
Walkthrough
Collect the Rocket Launcher to your right. Turn right, then head to the wall. Turn around, then shoot the Wall across from you to reveal a small alcove beyond.
Gallery
Exploding Wall - from The QuakeLab
Alternate Versions
Aftershock for Quake version using the Aftershock Level Theme.
Exploding Wall - from The QuakeLab (Aftershock)