A roundhouse is a structure which is used to store and service locomotives, along with other railroad equipment. Classically, roundhouses were literally round, explaining the name, although modern variations on the structure are often built in different shapes. A roundhouse may also be referred as an engine-house, and most major railroad hubs have one tucked away somewhere on the grounds, as one never knows when a locomotive might need service.
The first roundhouses were built in the early 19th century, and they were round for a very specific reason: they were designed to fit over locomotive turntables. Early locomotives did not run backward, or ran backward very slowly, so when trains needed to turn locomotives around, they were driven onto a set of rotating track which could be used to flip the direction of the locomotive. By mounting a turntable in a roundhouse, engineers could move the locomotives inside around very efficiently, creating stalls for each locomotive to be stored in and moving the locomotives into stalls with the help of the turntable.
With the development of modern locomotives which are more easy to maneuver, the turntable is not as necessary, although some railroads certainly still use turntables. However, the need for a sheltered structure to protect locomotives while they are out of commission is still present, and by tradition, such structures are called roundhouses even if they are not round.
Many railroads use their roundhouses to store backup locomotives, or to store locomotives while they are not in use. Depending on the size of the railroad, a number of locomotives may be kept out of service at any given time, allowing the railroad to be flexible about its train scheduling. When locomotives are damaged or in need of routine service, they are also stored in the roundhouse, which typically contains equipment for working on trains.
Touring a roundhouse can be quite exciting, especially when the structure belongs to a large and busy railway company. While locomotives are not quite as picturesque now as they were during the days of steam, they are still quite impressive. The staff of the roundhouse are also often very enthusiastic about the trains they work on, and they are usually happy to talk to people about the locomotives and to give guided tours of the equipment used to work on them.