Splashing through thigh deep water, the ceiling barely a cubit above your heads, you exit through the squarish doorway into a squarish passage with an upward floor. The passage leads up out of the water and curves to the right. The ceiling remains low.
You come to a point where another passage meets the one you're in, the two passages joining in an arrowhead shape. Facing the point of the arrow, you confront a rusty door. It is closed. The other passage goes kind of backward and left from here.
What do you?