Netherglades
Not to be confused with The Neverlands. This is an area on the Circle Sea coast of Quirmwhich appears to be continguous with the maquis country described in the text. A substantial loop of the railway runs through here. Interestingly, we are informed that one other local peculiarity that absolutely meant the railway had to be re-routed in Quirm was a whole area completely inhabited by Zombies. No other information is given by Mrs Bradshaw. It is described in The Compleat Discworld Atlas as a place with little dry land, none of it permanent, where the indigeonous people live and work on rafts, even mooring rafts to act as cultivatable gardens. The Society of Apothecaries is really excited by the Netherglades and describes it as "the natural pharmocoepia of the world".
Annotation
On Roundworld, Zombies are strongly associated with tropical or sub-tropical areas once colonised by the French: Haiti and Louisiana in the Carribean. This appears to be another of those places analogous to parts of the Americas which Sir Terry once deceed that the Discworld should not have.