What worked for me:

PCs are running away from a group consisting of around 50 armed soldiers, try to hide underground - and find a passage to an old necropolis. The usual "all who enter will be doomed" warning carved above the door gets ignored. The scrawled "light makes shadows" not so much.

One or two of them catch a glimpse of a person in robes standing just so they catch it only by the corner of their eye. When they look, there is nothing - only a statue, tomb or something like that.

They have only one torch - and few candles. They decide to go in darkness and try to use the candles/torch only in case of emergency. They bind themselves with rope to not get lost and continue.

I only describe what they hear and what they go through - cobblestone, water, something crunchy (they tried to pick it up... human skull.... child skull).

Suddenly they hit a big door - the leader asks me what he hears... I play him (and only him) a sound of child, sobbing.

They light the torch and enter. They find the only illuminated place - a circular room full of mirrors, with a column of light in the middle, coming from above. On the floor they find a map of the necropolis, which they study a bit and find a way out. Then they start to get comfortable - eat something, rest a bit...

I tell them they are feeling very comfortable - almost like they feel that they don't want to leave. Ever. And a perception roll tells them they start to see figures appearing in the mirrors...and that the dust on the ground is thick, almost as if it wasn't only normal dust.

They get the idea and leave.

The exit point is a tower on the opposite side of the necropolis. They manage to find it. They light up a torch - and enter. The shadows seem to flicker a lot.

First hall? Hall of echoes. Their words echo. Stairs, with windows. They see only darkness.

Second floor? Hall of different echoes. Their words become twisted in the echoes. "We should hurry" becomes "...should stay." "What was that?" = "What am I...?".

Third floor? A balcony. They see the 50 men enter via the door they entered on the opposite side. Most carry torches. There is enough light.

The darkness swells around them and just swallows them. The lights stay, but now there are shadows...

...and as they carry the torch, the shadows step out of the walls and attack...

Let's say, ever since then, it's enough just to say "the shadows flicker a lot..." or "the shadows seem strange..." and they stop and usually dump the light.

...oh, and I let them re-explore the dungeon once more later