The Deepmaw
The Deepmaw are a location in the vicinity of Fort Sinister in the Fallow Marches.
Traveling five miles west of Fort Sinister, one discovers a large grassy hill rising out of the Camwood. No trees grow here, and up until fifteen years ago, it was a popular pasture for the local farmers. Then the top of the hill collapsed.
Directly beneath the surface of the hill lay the secret, undocumented prison of House Glamourous: the Deepmaw. Fifteen levels of illusion… and ghost… and undead haunted abandoned prison. The farmers refused to return. Adventurers flocked to it. Deepmaw Mercantile was set up to service the dungeon explorers.
Eight years ago, the adventurers reported that a large chunk of the bottom level had collapsed as well, opening up a vertical shaft connecting to yet more subterranean levels: seven floors of Slumbering or perhaps Divine Era vintage, with all the bizarre monsters and animated artifacts one expects from such. And by the way, the shaft keeps going down.
While the intrepid explorers haven't made it beyond the second layer (at least none that have returned), they have managed to scry and send familiars into the depths. Half a mile below, the shaft opens up into a vast cavern, dimly lit by naturally luminescent crystals and unnatural fungi. And at the bottom, if the reports are to be believed, are the ruins of an equally ancient village, and a river thought to be fed by the Longfalls many miles distant.