I announce "Oh, this is a fun room," and start drawing the room dimensions on the playing board.
The room is a 30x60 space, with huge puddles of flammable oil on the floor. Oil drips from the ceiling in several spots throughout the room. At each corner, there are stacks of wooden barrels. Black powder can be seen near and on the barrels. In the center of the room, where no oil is dripping, ten zombies are huddled together. On each zombie's head is a lit candle.
The PCs can gather this much information:
1. There's enough powder kegs in each corner to blow up the room. Given the support structure of the dungeon, that would probably cave in several surrounding rooms and corridors as well. And it might block their only exit.
2. If the oil ignites it most likely will set off the powder kegs.
3. The oil is slick and zombies are clumsy. If a zombie slips and falls, that might be curtains for the room.
4. The candles are somehow magical... how else would they still be lit after who knows how long?
I sit back and smile with anticipation, waiting to see what clever, ingenious plan the PCs are going to come up with in order to defeat the zombies without blowing up the room. I can't wait to see what antics they will get into just to avoid setting the oil on fire. I imagine them blowing out the candles as they fight the zombies, or hacking apart zombies only to to catch the severed heads before they hit the ground. I imagine the sorcerer using his boots of levitate and ray of frost just to put out the candle flames... I am really excited about this part of the game and...
...the PCs close the door and say "We'll come back to this one... later."
talk about being a crestfallen DM.