===== Return to Bald Mountain =====

the big blank space in the 1st level of the floor plan just screams "find the secret door"
Hmm

But it makes sense with what's above it
Some sort of water pouring in and dow
Ya it's supposed to be solid rock
But i suppose a secret room would be interesting
Actually it could be a whole separate adventure

The wizard encounter room has a bunch of floor drains
And it's above that blank space
Maybe add a small water wheel or something
Yes and my world already had a substantial underground  motif

Like the water is flowing and powering some arcane device
This could be another entrance to the underground city
That's perfect
I will add a noise of creaking machinery

It also adds incentive for the wizard to want the weather
It is sealed by an ancient spell and he need time to figure out how to break the spell