I'm in the moathouse, and the ogre is in the other room, but I cannot climb the stairs. Anything? I had heard there was a way, but clicking on the stair icon does nothing, which is as stupid as it sounds.

In a large area, combat automatically ends if you manage to get your entire party far enough away from the nearest hostile creature. I don't know of any way to leave the map during battle though.

However, if you haven't alerted the ogre to your presence (read: you saw him with a sneaking rogue, and turn-based mode hasn't begun) you should indeed be able to climb the stairs.