No terrain is impassable for a determined human being!
1:The human expansion during the last Ice Age.
2: Marco Polo’s travels of 1271 to China
3: Columbus’s journey across the Atlantic Ocean to the new world in 1492.
4: The expansion of settlers during the late 17 hundreds and early 18 hundreds.
5: The Arctic and Antarctic polar expeditions of the late 19th and early 20th centuries.
6: Humans landing on the Moon in 1969.
If somebody want to get somewhere bad enough, they WILL FIND A WAY!
It just needs to slow them down. Few Italians are moving to China now and not many people are moving to the poles or the Moon.