MeepoTheMighty said:
How's he going to fill the room with water?
There was a waterfall about 200' away.
The party was away for 12 days, enough time for the bad buys to make the walls, build the flue and fill the rooms.
If it was a day or two, the party would have just seen the walls going up and a partial flue.
Well, I did it, and they lived.
Nice surprise though.
I allowed the Reflex save for holding breath, DC 15.
All but one made it, and that one got 1/2 their CON, rather than their full CON.
I set the DC for doing spells underwater at 20+spell level.
I figure that if it's the same on a ship in a storm, it would be the same underwater in calm water.
This allowed the party to survive, they tried 6 spells and half of them failed (10th level party)
I would probably should have done DC 25+ spell level, but I don't like killing parties.

They had to roll a swim every round, of course. Love those encumberance minuses to swim.
They tried to break through the wall, they tried to block the incoming water, they tried to swim to an air pocket.
All failed.
Finally, after about a minute, they teleported out.
Made some magic items and came back a week later to a different point in the dungeon, kicked butt, took names.
They had fun.
'Course now they're trapped in a 15 x 15 room until the sorcerer can do her spells the next day.
There is a 14 inch hole for air, etc, though.
Trying to figure out how to get the bad guys to keep them awake so the spells don't get memorized.
Wish me luck.