Looking up at the hole in the Pantheon ceiling, Rome. Dating from around 126 BC, this former temple has been used as a Catholic church since the 7th century. One interesting bit of trivia: the height from the floor to the oculus (the hole) is the same as the diameter of the interior of the room: 142 feet (43 meters). And despite it’s age, the Pantheon’s roof is still the world’s largest unreinforced concrete dome.