I saw this film years ago, but I can't remember the title. The whole film happens inside a room, it's about a guy who tries to convince others in the room that he is immortal (or maybe very, very old). I remember the film blew my mind, but somehow I can't remember the title. Any idea what it could be?
This could be the 2007 movie The Man from Earth:
The plot focuses on John Oldman, a departing university professor who claims to be a Cro-Magnon (or Magdalenian caveman) who has somehow survived for more than 14,000 years. The entire movie is set in and around Oldman's house during his farewell party, and the plot advances through intellectual arguments between Oldman and his fellow faculty members. The movie is composed almost entirely of dialogue.