The dungeon isn't four-dimensional, but it's very aggressively three-dimensional, a maze of twisty passages laid out like a deranged ant's nest, built out of attractive exotic minerals in swirling blues and teals and ice-whites (which are being aggressively mined closer to the entrance; they'll sell as decorations even if they have no interesting materials-science type properties). The monsters aren't nearly as pretty. Because they're big nasty centipede things with double sets of scary pincers.

The big nasty centipede guarding one particular crevice in which one particular prisoner is waiting goes down to the sound of gunfire.

The associated esper pops into view a moment later. "Hey there! Can you climb out without the centipede in the way or do you need a hand? Water or anything? I'm Traceless, if you haven't heard of me the deal is that the monsters can't see or hear me, but that doesn't extend to you, so on the way out you're gonna want to stay close and behind me and if any get in the way I'll kill 'em, but this lot are not crawling around away from their assigned guard duty too much, so probably we're gonna follow the spraypaint marks I left without running across any live ones, and be out of here in a jiffy."