Loqua

Loqua is a flat world of neverending oceans (with only a scant few archipellagoes here and there) that is especially unique due to both sides of its flat surface being inhabited. Both sides are mostly composed of water - and to move between them one has to descent to the deepest of chasms on the bottom of 'their' sea. At some point during said descent, gravity will suddenly reverse - and the rest of the travel is the ascent.   Only one side of Loqua acts as a seat of civilization - it's mostly a relatively pleasant sea, with lifeforms that wouldn't be unheard of on Earth. It's approximately 2/3 various degrees of warm (and with tropical isles on top of it), and 1/3 relative harshness (more like a temperate or cold parts of Old Earth's seas). In short, a more or less decent place to live when you are an aquatic sapient with an intent to live a long life.   The Inverse Sea is significantly harsher, with numerous alien beasts prowling it (some of which can possess impossible skills - or sizes). It is inhabited, theoretically, but only by a few communities of outcasts or thrill-seekers. The non-sapient lifeforms from the Inverse Sea do not attempt to enter the other one, but servitors attempt it from time to time (whenever they managed to assemble some numbers without local life devouring them whole.