I'll preface this by acknowledging the fact that some in-game models don't have backsides/etc to them. Those can stay facing forward if so desired.
Dungeon rooms in the underground always appear to have a specific orientation, usually facing northwards. I'm proposing a randomization of room rotation so that such areas appear different each time they're encountered, while still containing the same assets.
It sounds like a cheap way to do things, but it'll make a noticeable difference if implemented correctly. Hallways might have to be stretched and walls relocated to support accessibility and the camera angle (respectively), but as for the interactable portions of the room, moving them 90/180/270° on the Y axis would be refreshing to play through, as this would ensure memorization is turned on its head. In the literal sense.
I'm pretty sure most assets like walls, passages and corridors already have a variation of possible directions they could be facing, so it could be tested on clockwork tunnels first.
It's kind of tricky but it would multiply the level variations right of the bat.