Heard Island and McDonald Islands (ISO 3166-2:HM) is one of the most difficult countries/territories on ISO 3166 for any human to legally set foot on. You would probably have to organize your own scientific mission in order to be granted access. Our crew member,
@icetrek Eric Philips, was lucky enough to set foot here in 1996.
Another is, remarkably, U.S. Minor Outlying Islands (ISO 3166-2:UM), as the
@USFWS has not issue any permits in recent years, with a notable exception of President Obama’s visit to Midway Atoll in 2016. I also searched for Bouvetøya (ISO 3166-2:BV) while in orbit, unfortunately, it was covered by clouds.