I know that there's Sothoryos and Ulthos, which you can read about on the ASOIAF wiki. Those are the most "remote" lands in ASOIAF that we are aware of. Then there is the far east like Ying & Yi Ti which aren't "Unknown" lands, but they're just so far away from Westeros that you get mostly fantastical understandings of those areas (here be dragons) and then there are remote places like Mossovy and Mountains of the Morn, Bloodless Cities, Land of the Shrykes, etc.

Alt Shift X has a pretty good video on the Strangest Places in GOT too that might help.