The Waterway is a vast sea in the Underland. It can be accessed from Regalia by the river. Gregor and the quest party travel it on boats in The Prophecy of Bane. It is likely too large for most fliers to fly across, but it's never been attempted. There are two gateways to the Overland over it, one of them leading to Central Park. There is a freshly formed island about halfway across, inhabited by flesh-eating mites. This island is originally thought to be the origin of the Plague.