Just saw this interesting little piece over on The Daily Grail. Apparently a researcher from New Zealand was visiting the Pantheon in Rome, when he discovered that the entire building could be used as a giant sundial.
According to this article in the New Scientist,
"...the Pantheon may have been more than just a temple. During the six months of winter, the light of the noon sun traces a path across the inside of the domed roof. During summer, with the sun higher in the sky, the shaft shines onto the lower walls and floor. At the two equinoxes, in March and September, the sunlight coming in through the hole strikes the junction between the roof and wall, above the Pantheon's grand northern doorway. A grille above the door allows a sliver of light through to the front courtyard - the only moment in the year that it sees sunlight if its main doors are closed."
While it might seem a little far-fetched that an entire temple was oriented so that a single part of it was illuminated at noon on one day of the year, it's still pretty cool. Plus it reminds me of this, from Indiana Jones:
Damn that was an awesome movie.