Duke 3D: (clipping) Normally inaccessible passage can be crouched into on E2L4 (Fusion Station)
This was caused by SVN revision r7488 (commit: 422afced). This particular alcove in E2L4 shown in the screenshot is not supposed to be accessible, as the player is intended to shoot the switch through it. As it stands however the player can simply walk through unhindered.
Here's a cutout of the offending map portion: crouch_clipping_check.map