I couldn't figure out how to get to the bottom-left corner of the map, despite the tantalizing marking of the ruined tower. Finally, I found a place where Lae'zel could make a leap across some jagged rocks. The other characters weren't strong enough, and although they are carrying about 1000 feet of rope, she had to explore alone. Killed some fire fungus, and then found a place where I could jump up shelf fungus on a wall. The first time, one broke and I was stuck, but I reloaded and was more careful to cling to the wall and made it all the way up. From there, there's a teleportation portal back down -- ah, and up again (if I'd just gone there first could I have saved all the jumping?). And there's a fake wall which leads to a portal in to the swamp. Soooo, I fast-travelled the rest of the party to the swamp, and had them meet up with Lae'zel there, and then everyone hopped back through the portal, walked through the illusory wall, and then the other portal down.
That all seems a little silly.... was I supposed to do this another way?