Papua New Guinea
In early 2019, I undertook a two-month journey through the interior of Papua New Guinea. The goal was to get from the coast (at Lae) back to the coast (at Wewak) via the country's highest peaks and having paddled the longest river, the Sepik.
Some of the challenges en route included dense virgin rainforest, monsoon rains, tribal violence, whitewater rapids, crocodiles, and some of the world's most inaccessible places.
The journey was certainly a physical challenge, but that was merely due to the only available means of travel (human-powered) in one of the world's last true wildernesses. The real interest of the journey, however, was the peoples and cultures encountered along the way. Due to incredibly inhospitable terrain, geographical isolation, and international neglect, PNG is unusually dislocated from the developed world and has an uniquely well-maintained way of traditions and customs.