A waterfall located in the midst of a larger body of water that pours continuously inwards — as if rushing over the lip of a suddenly submerged cup. Logic dictates that water flowing over the falls should fill the basin into which it flows. But through some means a void remains, and the falls continue to flow. The physics behind this phenomenon can be handwaved away with environmental magic, or the author can conjure up a high tech, super-efficient water recycling machine that somehow keeps the basin from flooding. The space at the center of these waterfalls seems to be coveted real estate, drawing all sorts of examples of Bizarrchitecture. Can be the mark of a not-quite-so-underwater Underwater City.
Dramatically speaking, there's always the possibility that whatever machinery or magic drains the basin will break and the protagonists will be faced with a rapidly flooding arena. Whether or not they can swim is a different story.
Sister trope to Waterfall into the Abyss, in which water cascades off the side of a Floating Island or the edge of a Flat World while being fed by a seemingly inexhaustible source. Also related to Mega Maelstrom, which is mother nature's version of this but with spinning. Can lead to an Inevitable Waterfall moment, even in the middle of an ocean.
- One Piece: During the Enies Lobby arc, Robin is being held on Enies Lobby, an island hanging in the middle of an abyss by a narrow strip of land far too frail to actually support it. The abyss is in the middle of the ocean, which drains eternally into this bottomless pit.
- The Adversary Cycle. Played for horror in Nightworld where portals to Another Dimension have opened sending nightmare creatures swarming across the Earth. Some of them open in mid-ocean, swallowing ocean liners and creating vast whirlpools during the day and reversing at night into mile-high fountains of water, littering islands with dead fish and...other things.
- A glitch in Assassin's Creed IV: Black Flag can cause the water under the ship Jackdaw to render incorrectly or not at all, resulting in a steep-sided hole in the ocean where the ship ought to be.
- Final Fantasy XII: The Ridorana Cataract is a huge sinkhole/whirlpool at the eastern edge of the sea that prevents access to the land beyond — ordinary ships get pulled into the cataract, while regular airships lose power if passing over it since the whole area is a jagd.
- In Guilty Gear, this is what Japan has become after getting wiped off the face of the Earth by the command-type Gear Justice. Its most notable appearance is as a stage in Xrd.
- Luigi's Mansion: Dark Moon: The Treacherous Mansion miraculously stands on a very precarious rock in the middle of a giant sea sinkhole.
- One of the unlockable friend areas in Pokémon Mystery Dungeon: Rescue Team is the "Enclosed Island," which houses Deoxys. It appears as a rocky outcropping in the center of a circular waterfall◊ with a single narrow path leading off screen.
Description: An eerie light encloses this rocky island, keeping out the sea. It is as if the island is in another dimension.
- In Adventures of the Gummi Bears episode My Gummi Lies Over the Ocean, Gruffi and Tummi are stranded on an island in the middle of a hole in the ocean, surrounded by falling water◊. Unlike other examples, the water is filling up the hole, threatening to sink the island. Gruffi and Tummi — and a third Gummi, Gusto, who was stranded years before — have to figure out how to get back home before it does.
- Steven Universe: The Lunar Sea Spire from "Cheeseburger Backpack" appeared as an intricately designed tower at the center of a watery sinkhole somewhere in the Northwest Atlantic ocean, glowing with an unnatural light that underscored the mystical nature of the structure. As the episode begins it is revealed that centuries of neglect have taken their toll on the structure, and the mechanism that has kept the waters from closing in on the tower is about to fail. Pearl mentions that the "moon goddess" statue that was taken from the top floor of the spire is the only thing that can reverse the damage and save the spire from destruction... but the Crystal Gems are ultimately unable to return the statue to the spire, and must beat a hasty retreat as the sea sinkhole closes up and the structure is swallowed by the waves.
- Bell-mouth spillways found in reservoirs around the world. When the water level is low, the top of the spillways look like inverted trumpet bells stick out of the water. When the water level is high, it looks like a hole has opened up in the surface of the water.
- The National 9/11 Memorial features two recessed rectangular "reflecting pool" fountains set in the footprints of the Twin Towers. At the center of each pool is a smaller square waterfall that seems to disappear underground. The edges of the larger pools themselves are are much taller waterfalls that cascade inwards.