×get to the area at the northwest so as to dispense with the goblins

×
I dispense with the fewest number of wraithwings possible (3 - 4), go northeast to "1" and stop at "2". I am certain the next step is to head towards the area denoted by "3", but I never make it all the way there alive since I'm surrounded by goblins. (I once killed one of the goblins at "2", but I've never been able to repeat that.)

×
What you want to do is get to where I have marked 1, then fanagle the goblins so that none of them are directly SW of you when you step out. I don't know exactly how to get this to happen (sorry), but I just kept slightly altering my path there until it worked out.

Anyway, once you do that, move to 2 (or somewhere else on the same diagonal. Here's the trick: move SW from 2 until you line up the trap door at 4. Once you get there, get rid of the rest of them, and you should be home free.