How do I get out of the swamp?

I finished the rogue. exited down to the light swamp but can't get beyond it. I got left one screen to a place with 3 bridges but there's no way out, only back. It's been 4 hours now and I'd like to get some sleep! Can't remember how I got there because that was 6 hours ago! I don't do maps very well, I just keep going around in circles.
On the positive side, they are all level 20+ with over 200 HP each.
Can someone please help? I've tried getting Marnie to jump on the black islands but it only goes a jump out and back (it's where the altar is).

On the positive side, they are all level 20+ with over 200 HP each.
Can someone please help? I've tried getting Marnie to jump on the black islands but it only goes a jump out and back (it's where the altar is).


