I found out that beyond the platform of the final boss in the dungeon, there's a neverending barrierless zone that looks like the inside of EoE10.
I got there using the Rocket Boots Extreme + Rogue Sprint, coupled by the engineering parachute. Any slow fall will do.
What you wanna do is face the boss from the top of the staircase, then hit sprint and boots. Pop Parachute or slow fall immediatly after jumping. You should go over the boss and not aggro him. You will then fly thru a wall, and start to see whats in the screenshots. Good Luck, I hope you like exploring.
EDIT: I'm also using the Elixir of the Sage's rogue exploit for fun. 280 energy is boss. :P