If you’ve never heard of ‘Harold and Kumar Go To Amsterdam’ then you’re not alone. The short film was revealed to exist back in 2006 but it never surfaced until the DVD for Harold and Kumar Escape From Guantanamo Bay was released with extras.
You can watch part one above and the second half below. Keep in mind that they are censored.
Because this film is more like a fictional documentary of a trip to Amsterdam, my guess is that this footage was compiled during the shooting of the second movie. Obviously the cast and crew had a wild time; and what better way to do it than write it off a business expense?