Turn the lights off!

[Mistresss]

Figured that hiding your torch and putting room to darkness can reveal a loose soon-to-be-open walls. If there is a light source behind them, you can see them glowing a bit. That doesn't help you finding the switch, but tells the general direction where to look.

[FloorBelow]

Indeed. I have uncovered quite a few secret doors with this nifty trick.

[Aro]

That must be reason for a "darkness" spell to exists...

[sirchet]

Thanks for the tip!

[killington]

That must be reason for a "darkness" spell to exists...

It's also useful for a puzzle in the game, but not necessary.