The Caldonian Rail system consists of a pair of stacked tunnels that wind through and between each of the major mountain cities of Caldonia. Each tunnel is lined with two thin rails upon which sit the railcars which move in opposite direction to each other. The railcars pull graescence from the rails themselves, powering a variety of graetech within the cars, causing the cars to hover above the rails, and providing power to accelerate the cars along the rails.

The rail system is made of thousand of tunnels that branch off and feed back into two main lines. Despite the proximity of the upper and lower rails, they do not connect— there is no way for a car to move from one to the other without having to be taken apart and reassembled.

No one knows exactly who built the rail system—that truth long lost to ancient history—but most agree it was built at the same time as the mountain cities.

Most parts of the railcars have been replaced repeatedly over the years, all except for the rail tech. No one has successfully figured out how the rails work, nor replicated the design despite its apparent simplicity. While current tech can replicate the feat of hovering and even moving at slow speeds, it breaks down at higher speeds, causing the cars to derail.

Nobody knows why (or how), but the cars generate a series of tones when they're in motion: a high whirring and a low thrum. Most engineers suspect this is the key to making the tech work, though, again, they've never been able to replicate it.

Most of the cars in use are designed for short term travel, with a lot of standing room and simple benches lining the walls. These are generally free so long as you are in of the proper social standing.

Long distance cars moving between the cities tend to be much more luxurious, often featuring beds and comfortable seating. Travel on these are paid for, usually expensive.

There are thousands of railcars. Each car can take anywhere from ten days to over a month make a complete circuit, depending on the route they take and the stops they make.