The Caldonian Rail system consists of a pair of stacked tunnels, each lined with two thin rails upon which sit the railcars. The lower rail moves clockwise, while the upper counterclockwise. 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. All of this is handled by the driver in the lead car.

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, but most agree it was built at the same time as the mountain cities. The truth has long been lost to ancient history.

Most parts of the railcars have been replaced repeatedly over the years, all except for the rail tech. No one has successfully recreated that tech despite the apparent simplicity of the design. 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 that is more felt than heard. Most engineers suspect this is the key to making the tech work, though 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 are much more luxurious, often featuring beds and comfortable seating. Travel on these are paid for, usually fairly 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.