Built between 3100 and 2900 BC: at the winter solstice the chamber inside is illuminated by the sun.
I think the instant of the Solstice this year is 17:47 UTC
In Los Angeles: 09:47
In New York: 12:47
In Melbourne: 04:47 on the 22nd
Edit: I've always wanted to take a picture of it, but I've never had a spare camera I can bolt down for a year...