You can't find it. It's gone. So, you forget about it. And then one day you get lost at sea, you wander too deep into the woods, your starship's hyperspace thingy malfunctions, or you just fall through a metaphorical crack in the sidewalk, and you end up discovering where all those missing socks go. Charles Fort called it the Super-Sargasso Sea; the dimension into which lost things go. Amelia Earhart's over at the bar. The Lost Colony of Roanoke is next door. USS Cyclops? In the harbor. Elvis? Who do you think is on stage? The Dead Sea Scrolls? Have a pamphlet. And everybody has all the socks they could possibly need. Just not matched ones. This is a place all adventurers In Harm's Way wish they would end up, and everyone else wishes was just a fantasy; the multiverse's biggest attic/basement/toolshed. Everything is here. Starships, Indigo Children, misfit toys. It's a Portal Crossroad World where it's easy to enter but significantly harder to leave. It's a Derelict Graveyard that people actually live in. It's a Landfill Beyond the Stars where the crap never stops gathering. It's everything you could possibly want mixed with all the stuff you hoped you'd never see again. Often accessible via The Bermuda Triangle.
- J. Michael Straczynski's Midnight Nation is a place of the lost and abandoned — not just objects but people. A particularly interesting element of that is a shack containing the lost work of every artist who died before creating it, kept safe until such time that another artist can create it.
- Daring Do and the Journey to the Center of the Earth has the Temple of the Lost. The protagonists go there to find Pinkie Pie's missing body, and they have to sort through loose change, missing socks, and other assorted junk first.
- Sakaar in Thor: Ragnarok; in the Marvel Cinematic Universe, any Blind Jump will add you to the endless stream of junk falling from the myriad portals hovering above this Landfill Beyond the Stars.
- The Land of Lost Objects in Eerie Indiana is located in the center of the Earth and is run by the US government that steals objects to promote consumerism.
- An episode of Charmed has the Halliwell sisters using a spell to find lost things backfiring to the point that everything they ever lost came back, thus turning their house into this trope.
- In Ben Lear's Lillian: A Folk Opera, the narrator believes that everything lost winds up eventually in the Great Pacific garbage patch. He journeys there to find a vague something that he thinks is missing from his romantic relationship.
- Dark Void. Aliens, lost ships, Nikola Tesla. It's all in the Void. The hero even enters via The Bermuda Triangle.
- In Touhou, the barrier surrounding Gensokyo works such that it attracts things or concepts which have "become fantasy" in the outside world. While it's mainly a justification for the existence of youkai, it also attracts other things like extinct or endangered species, and yes, a bunch of lost items from the outside.
- Dungeons & Dragons (BECMI) module IM 3 The Best of Intentions. One of the planes the Immortal P Cs may have to travel to is Unsoncy. The center of the plane is a rotating disk of debris that comes out of a singularity in the middle. Items lost on other planes of the universe end up here. The Immortal who controls the plane always looks here first when he loses a pair of socks in his washing machine.
- On the search for Cassie's missing dad, Marion and Cassie from Bounty Hamster find themselves in the world of the lost. Not only are lost objects there, but people too: there's a room of lost dads and even the antagonists that the duo 'lost.'
- A sock-oriented variant appears in one episode of Jacob Two-Two. Jacob finds an Alternate Dimension where all the missing socks go. Here, they use socks as currency, and there's even a black market for them.
- A literal Land of Lost Objects appears in The Real Ghostbusters.
- In Peter Pan & the Pirates both the Lost Boys and the Pirates enter a group of caverns in Neverland that is indeed the Land of Lost Objects, where they even met Captain Hook's lost childhood.
- In The Ren & Stimpy Show episode "Black Hole", Commander Hoek and Cadet Stimpy go through a black hole and end up in a strange dimension, where they find a pile of all of Earth's missing left socks.
- The Bikini Bottom Triangle in the eponymous episode of Spongebob Squarepants contains many items taken by the mermaids via singing to activate a giant vacuum, which opens a rift in the sky while doing so. When they sing their song backwards, the items are returned to their owner.
Hello, Unknown Troper. You'll need to get known to lend a hand here.