If traversable wormholes exist, they could allow time travel. What is left is the Ellis wormhole, a nongravitating, purely geometric, traversable wormhole. For humans, they make dense, impassable forests traversable. Examples of apparent FTL proposals are the Alcubierre drive and the traversable wormhole. The Ellis drainhole is the earliest-known complete mathematical model of a traversable wormhole. A freely traversable walkway divides the station into two sections. The small size of the village makes it easily walkable and traversable by bike. From 1906 until 1987 there was also an active foghorn, which is traversable in azimuth. Fire, Freeze, and Change, which turns large gems into traversable blocks. If such a walk exists, the graph is called traversable or semi-eulerian.