Remember "the others" on LOST and how everyone feared them? There is a "lost tribe" on North Sentinel Island that will instill more fear into anyone who tries reaching North Sentinel Island. No need to care to heed any travel warnings by the United States State Department or otherwise. Just read about two fishermen being killed by the natives of the island when their boat accidentally got to shore.
This particular tribe of Sentinels will not look curiously as a foreigner approaches despite being isolated from other humans for centuries. While someone might bring them a gift, their idea of gift in return to any outsider is a bow and arrow. The reward for someone stomping on their turf? Death.
North Sentinel Island is a part of the Andaman and Nicobar Islands in the Bay of Bengal between Myanmar and Indonesia. It is mostly covered in forest, where the violent natives hide. It is surrounded by coral reef. There is no organized travel. It truly, and sadly because it may just be a beautiful place despite the natives, deserves the title of hardest (maybe even most dangerous) place to visit.