you can only get here through the pit on the island in Quagmire Estates.
this dungeon is INCREDIBLY frustrating. i do a lot of messing around with Teleport Scrolls, Ethereal potions, and Passwalls. the @ switch is a shortcut - flip it, then find the stairs marked with @ signs.
there are a lot of useful scrolls lying around - you can get them faster with Grasp (shift-G), but i like to use them as sort of a reverse breadcrumb trail, to see where i haven't been yet.
they did actually release an annotated map: check here.
by abby, fucking around in 2021. made with love, powered by sugarfree red bull.