A Brief Guide to the Thalassium

 Everyone has heard stories about people swallowed by sea monsters, living there for months or years before miraculously returning to civilization. These stories are all false. Not the part where they survive being swallowed, the part where they come back.

The Thalassium

This is where old sea monsters dream. This is where the things they swallow go. It is the ocean as seen by a leviathan. For them, the deep is not dark, so you can see as well, alien sensations of distant  currents and unfamiliar wavelengths of light translated into anti-colors. Almost-greens, nigh-purples, and not-blues, opposite of pale. You can breathe, of course. Sea monsters don't understand drowning.

Sea Monsters

They're not really here most of the time. They used to be, long ago, before they've grown ancient and huge. The world was different, then. Richer in life. Now if they are to sustain their massive bodies, they must keep moving at all times. Rest cannot be afforded. The most they can manage is a fitful half-sleep, when their massive, transparent visages flow through these unreal depths. They're impossible not to notice at these times. The space around them is more vibrant and fluid, changing according to whatever new sights and entered their tired minds since their last lapse of consciousness

Obviously, the dreamselves of colossal sea creatures, sluggish and not fully material as they may be, are still dangerous. Getting eaten again, or pushed into some underwater fixture with terrible force remain very real possibilities. What happens after is unclear. Maybe you just die. Maybe you're thrown into another, deeper layer, further still from mainline reality. Regardless, if an unfortunate survivor wishes to avoid such a fate, they need to seek places where sea monsters don't go. And in their own dream-world, there are few options.

Nightmares

It's hard to believe creatures so big and dangerous could fear anything at all. They do, of course, like every other living being complex enough to think, and over the course of their long, long lives they've amassed quite a few of them. There are old fears, simple and primal, from the time when they were not the biggest fish in the sea. Fears of predators and men with sharp spears. As they aged and grew new fears set in. Of stumbling into a barren stretch of the sea and starving before they could escape. Of sudden algae blooms which could unexpectedly poison the water around them. Of their constantly nearing end, abstract and indistinct, but inevitable.

These terrors manifest in the Thalassium. They are the leviathans' nightmares, places they avoid, places they don't control. They're rarely, if at all, hospitable. Still, stranded sailors don't have many alternatives. They built their ramshackle shelters from the hulls of shipwrecks and scavenged rope, right next to fuzzy, exaggerated memories of prehistoric sharks and bleak patches of nothing, haunted by an alien unease.

People

You can find them everywhere, and so you can find them here. Almost none are here by choice, aside from a few weirdoes who wanted to be eaten by a sea monster. These are usually the mad hermits attempting to commune with monsters of legend, until they get eaten. The rest are mostly sailors, hardy folk. They're generally somewhat brusque and slightly manic, as if high on their continued survival. After a while people tend to reach the conclusion that clothing and other customs of the land are no longer applicable. Their shelters are wild and merry places. Scavenged alcohol is drunk, exaggerated stories are told, generally reckless and unsafe behaviour is engaged in.

The stories are important. To continue to exist in another creature's dreams they have to leave their mark. Impose their own version of reality. The bravado, the stories and chanties, help create a bubble of possibility, where survival against overwhelming odds is a bit more probable. This has the side-effect of establishing sailors as something equivalent to mosquitoes you can't get rid of in the leviathans' minds. As a result, survivors are at risk of gradually becoming caricatures of themselves, little more than erratically twitching, screeching shadows with sharp needles, what the sea monsters see them as. Remembering one another helps, but that can mean they just become exaggerated tall-tale characters instead. Preserving one's self is hard work in an unreal world.

You can't leave. Some tried latching onto a sea monster's dreamself while  until it awoke. None returned. Maybe that's just not the way it works and they got stranded too far away to return to shelter. Maybe it did work and they returned to the familiar problem of drowning all alone in the middle of the ocean. Going even deeper might be an option. Who knows where getting eaten again will take you?