Time

Of the resources available to the players and their characters, time is the most valuable. Vastly so.

An environment is a living thing, where all of the elements within it are aware of one another and exist in stasis.
The biggest advantage the characters have upon entering any place is that they are undiscovered and unknown.
With every turn that passes, that changes.
And given enough time, the greatest powers and dangers will become aware of them.

If they are at all sentient, they will begin to prepare.

Given their own desires, and the wall of resistance they are now up against with enacting them in the current environment, they will almost certainly see the opportunity in this trespass.

They may welcome.
They may negotiate.
They may threaten.
They may hunt.

The players are every bit as much of a treasure to the things in this place as the those things are to them.

And this place is their home.
They have traversed it day in and day out for weeks, months, years, decades.
New sounds, new sights, new smells stand out as if they were emblazoned upon the walls.

What is in the rooms nearby? What is above? What is below?
How many of those hyena things are in this place? How many of them might be wandering around?

Any thief can open a lock.

The question is, how quickly?
In the last of their dim and flickering lamplight. Wrapped in a small room of cold stone, breath curling out in waves. Hands still shaking from a fight they barely won.

A turn goes by...

...and you hear scratching in the distance.