I may be getting my recollections mixed up with 4th Ed.
In 5th Ed cosmology, is there any consequences for crossing the equator between North and South hemispheres?
Just recalling Erastothenes measuring the size of the Earth, and wondering what Magi might encounter going to Syene to verify the well shadow at the appropriate time.
There may be a wall of incineration around the Equator.
And south of the equator may be another realm, possibly the realm of magic. But I think that's all educated speculation by magi, not something observed.
But if your magi want to repeat the Syene experiment, that's well inside the known Mythic World. Anywhere south of the Tropic of Cancer can demonstrate that behaviour on the right day (or days) of the year.
There is some question if the Axis Magica has a second exit in the Hypernestorian Realm. Also, there may be tunnels which let you go under the Equator to the Mountains of the Moon (which are in Africa, not the actual moon). Also, the ancient Greeks sailed around Africa, so they must have had some method.
Maybe, but wouldn't the south glow?
Best to go look. It's a radical idea, but sometimes it is fruitful to investigate.