At first glance, "Mirror Mirror" doesn't impress: there are many empty spaces, and the rivers are formed by straight lines... However, the author tried to create identical contours of land and sea on the surface and underground levels: it's clear that this was done manually (although there are programs that allow you to copy the landscape, or rather, create a landscape from miniatures). Well, maybe it's more fun to play than it looks...
And who is the author of the map? It's not on any of the well-known websites with map collections.