This is a large, muddy room with a small swamp on the left side.
A gigantic snake (MR 225) lives here. Since it is so massive you may
make a L1SR with a +8 modifier on Dexterity to not be hit that round,
although you may inflict normal damage. The doors magically close and will
only open when the snake is killed.
You may;
go back,
go to the door at the end of the room.