[m4rtink]

IIRC British antarctic service does uninterrupted 2 yer contracts. Not Mars or a submarine but still 2 years.

[Cthulhu_]

At least being outside doesn't kill you in those ones.

There's also earthbound experiments like Nasa's CHAPEA programs (https://www.nasa.gov/news-release/martians-wanted-nasa-opens...) but they only go up to about a year.

[m4rtink]

Bases in the interior can get -80 Celsius and lower during the polar winter. The British base is IIRC on the coast, so it might be less, but still very deadly if you end up outside of the base without proper equipment and supplies for any duration.