Waterfall 

Continually awash with water, both falling, flowing, and still, Waterfall is responsible for the production of most of the kingdom’s textiles, as well as food from the floating gardens, power from the hydroelectric plant, and valuable salvaged resources from the garbage dump. It is also regarded as the Underground’s most beautiful sector.

Springhaven

The second largest city in the Underground, and the capital of Waterfall. Shaped into many layers like those of a fountain, the city is constantly under the fall of rain, and operates most of the kingdom’s business sector, along with many smaller, more independent businesses. The Underground’s most specialized and selective school, the Magitech University, is located here. Once always bustling with activity, the skyscrapers and wide streets and back alleys stand completely desolate, no monster brave enough to venture through the Mushroom Maze to reach it.

Gerson's old crabapple farm

One might mistake the golden light showering Gerson's old crabapple farm for highly coveted sunlight from the surface. That's wrong of course, there's only a few select places where such light reaches into these depths, and here, underneath the glacier-fed lake on the surface, was certainly not one of them. No, this light was like that of the rest of Waterfall's, originating from magical crystals growing in the caverns' ceiling, albeit the most brilliant and luminescent cluster of them all. Gerson had stumbled into this cavern by pure chance an age ago, when most of Waterfall's residential space was still being carved out. Perhaps it was the relic of a bygone era, like that of the Ruins, or simply just the origin of all the crystals in Waterfall. None would ever know, for Gerson had sealed the chamber off when the world outside began warping.

Still, his legacy lives on, thriving in the faux sunlight. His crabapples grow sweet and juicy on the trees he tended to in life, his dust now nourishing their roots in his passing. The magic in their cores prevent them from ever growing rotten, leading to a treasure trove of crabapples littering the cavern floor, ripe for the taking should any adventurous, Hungry soul find their way through the old tortoise's seal.

Marshdeep/The Mushroom Maze

Once a town set within a large copse of ancient mangrove trees, well known for their cultivation and skill with fungi. The Mushroom Maze now stands in its place, and has taken over most of the northern section of Waterfall, fed by the fetid water and the monsters attempting to flee to New Home. No monster, besides the one that created it, has ever emerged from within.

Coastharbor

A completely underwater city set deep in Waterfall’s largest lake, home to many plant and water elementals, fish and amphibians, and other waterbound monsters. The floating gardens once dotted the surface of the lake, tended by its denizens, and many piers lined its shores, bringing merchant boats back and force across its surface. The waters of the lake have not stirred in years. If the Hunger crept beneath its surface, none seem to have escaped it.

Riverview

A widespread scattering of smaller villages joined into one by many bridges, stretched out and around the Great River and lining the edge of the Echoflower swamp. The keepers of monster history resided here, Gerson most notable among them, and the tunnels the villages spread across are well known for the beauty of their glowing crystals, home to such sites as the Wishing Room, the Constellation Overlook, and the Hall of Memory. The bridges here have largely collapsed through water rot and disrepair, both stranding and dooming any monsters that survived their collapse, and the crystals have grown dark, plunging Waterfall into darkness.

Echo Flower Swamp/The Dead Swamp

The former home of the prized and unique echo flower, long since extinct through excessive consumption and neglect. What stand in their place are carnivorous mimics of their form, speaking in whispers to draw prey into their trap. The swamp itself is nearly impassible, a stinking, backed up, completely dark wasteland of death and prowling predators.

Temmie Village

The cavern that the strange Temmie clan settled within is completely flooded, now, abandoned by the foaming, mindless horde of creatures that roam the swamplands.

Backwater Row/The Hydro Plant

A small settlement that rose up around the hydroelectric plant and the entrance to the Dump, largely populated by rodent monsters. The populus once sorted and regulated the outflow of trash from the Dump and maintained the plant, but were long ago hunted to extinction. The plant has become completely inoperable since then, and sits derelict beside the overflowing, toxic Dump.

The Dump

The runoff from the landfill aboveground, teeming with potential treasures. Monsterkind has plumbed its depths since it began to accumulate, and owe many of their technological breakthroughs to the tech they found among the garbage. It is a ruinous, hazardous waste, now, hunted by the insane creature that once was Mad Dummy.

Mistveil

The proximity of Hotland’s lava to Waterfall’s lakes created the hot springs that this resort town was built around, and they produce a mist so thick that the construction of a lighthouse was essential to navigate between the two areas. With no food to be found here, and the difficulty of the terrain, it has been almost completely overlooked by hunters.