A lot of Muunfel is left without a specific map of the area. The Timewilds of Synka used to be better known to cartographers, but because of the shifting nature of the region and its hostility to settlement, that knowledge has shifted to the coastline and not far inland. Going off the road in Synka is terrible luck, so says the superstition.
Another region that comes to mind is the vast forest covered by the Faelands. Some would argue this land doesn’t count as “unexplored” because it actively prevents anyone from truly knowing where they’re going. The local fae lords and the leaders of the whole nation are able to clear the roads for visitors, but they can also trap trespassers in an area that may not let them leave.
Most regions of Korvasin, Genfierz, and the North are pretty well known. Rutan’s desert and the lands beyond it were unknown until recently, but as the country gains more of a foothold in the international world, more corners of the map are being filled in to the west.