The world has many names, though none may be as appropriate as The Coin of the World, or simply The Coin.
The Coin is an enormous disc making its way through space. The sun bobs through a gigantic hole in the center on a roughly 24 hour cycle, melting the crust and causing tides of lava to flow in and out of the hole every day. A gigantic wall of ice covers the outer rim, marking a harsh boundary between the two habitable sides. Between the molten center and the frozen rim stretches a wide band of fairly temperate continents separated by vast, turbulent oceans and tranquil seas.
Many moons hover over the surface, sticking to no known orbit, casting the influence of their particular magics over what lands they will, when they will it. The moons themselves are manifestations, some say the very source, of different domains of magic. In certain places on the face of the Coin, the influence is so strong from a particular moon that unwary travelers could take a turn and find themselves having been transported to the surface of that moon, and looking up in the sky, they see the face of the Coin where they were standing moments before!
There are as many miles from the hole through the center to the edge of the rim as there are from pole to pole on Earth. This makes for a huge amount of habitable land and oceans on both sides of the surface. But this isn’t the only place the creatures of the coin have taken up residence. The core of the world is riddled with a labyrinth of tunnels and caverns, many extensive enough to house entire empires that rise and fall beneath the surface never knowing or to be known to those on the faces of The Coin. Often, these tunnels can lead explorers to their untimely death, treasures untold, and sometimes they can lead all the way to the other side of the world.
The most well known of these trans-surface tunnels are heavily guarded and used as trade routes between powerful kingdoms. The main entrances and exits are taxed and tolled so that only the richest of merchants, nobility, and guilds can legitimately make use of them. It is not unknown for those with the means to acquire access to side roads that may just happen to connect to the main tunnels away from the prying eyes of those jealous guardians.
The Coin of the World is an enormous place with more than enough adventure for even the heartiest of heroes.