This represents the door that Truman Burbank enters. It is a tribute to the central idea from the movie. Truman is a kind of revolucion, that opens our eyes. This door is the autencity, the reality of each one. There is no light, we can't see anything, just the darkness of the unknown, but there, right in there are the answers, the veracity of our lives.
This single door represents a lot, and it is a climb, tough, although, worth.