The Railroad is one of several factions in Fallout 4. It is, quite literally, an underground movement to support, help, and save synths from the Institute often by smuggling them out. However, because of the nature of The Railroad's missions, its actual location can be difficult to find as it's hidden. This can be a source of frustration for many players, especially since The Railroad upholds the idea of all synths having rights, which is something that many people might agree with.