Mhu Thulan was a region of ancient Hyperborea famous for its sorcerers. It was the dwelling place of the legendary wizard Eibon, as well as Zon Mezzamalech, owner of the Crystal of Zon Mezzamalech discussed in The Book of Eibon. Among the cities of Mhu Thulan were Cerngoth and Oggon-Zhai.
Mhu Thulan apparently corresponds either to part or all of modern Greenland in its preglacial days.
Before the end of Hyperborean civilization, ice sheets from Polarion spread over Mhu Thulan. The one recorded attempt to recover treasures lost to the glaciers did not end well.
The following stories by Clark Ashton Smith contain references to Mhu Thulan:
- "The Door to Saturn" (1932)
- "The Ice-Demon" (1933)
- "Ubbo-Sathla" (1933)
- "The White Sibyl" (1935)
- "The Coming of the White Worm" (1941)