The first thing Bryce thinks when he steps through the portal is, this is so on-the-nose.

It's an obvious thought that dungeons are all Backroomses, but this one is literally just the Backrooms.  It's yellow and vaguely gross and has tacky wallpaper and moist carpet and loud fluorescent lights.  It also has a little bivouac of SWAT guys, who hand him a spray can of microsoft-paint-bright red spraypant and tell him to leave directions back to the portal, and confirm with him that they're using one of the inscrutable coordinate systems that he knows, in case there's a situation that calls for something more sophisticated than "which way out."  (This place foxes GPS and rangefinders, but there's only so much a baby dungeon can do about arrows physically drawn on the walls.)

They mapped out some of the place already; the monsters are sneaky enough that it wasn't totally clear they were there at all, and some kidnappees were rescued without having seen anything, but then one of them reported spotting a four-armed seven-foot-tall slenderman-looking thing sneaking past an empty doorframe, so they're calling him in to scout out some of the unexplored areas.  If all's quiet and he runs into anyone alone, though, he's gonna bring them back rather than waiting for backup.

Toby's hanging back at the bivouac in case one of the slendermans comes for them there, so it's just him poking his head around the doorframe of the shaded room.