As any Dr Who fan will know, Appalapachia is the location for the episode in Series 6 called ‘The Girl Who Waited’, which also happens to be one of my favourites.
A planet which, for reasons I won’t go into here, has 2 different time streams running parallel but at different speeds. If you happen to find yourself in the faster one, then you age rapidly, several years in the space of a few hours of ‘normal’ time.