When I first moved to the island, I joined a friend in the Old City for a tour and lesson on the history of Puerto Rico.
When passing by this little section of town near Pigeon Park, my friend and native-turned-tour-guide said that this was the smallest house in Old San Juan.
Wow, okay, so this little yellow portion is technically a house?
I've visited this site several more times since then and have never actually seen anyone enter or leave this door. Whether it's true or not, it makes for a cool story and great photo.