A Brief Guide to 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.