Manhattanhenge
“On Monday, May 28 the sun will set in the centerline of every NYC street. American Museum of Natural History astrophysicist Neil DeGrasse Tyson describes this phenomenon beautifully in the Natural History Magazine, explaining that like Stonehenge where the sun sets in alignment with stones during the summer solstice, Manhattan has two "special" days where the sun sets between buildings - May 28 and July 12: On these days, the Sun fully illuminates every single cross street during the last fifteen minutes of daylight and sets exactly on the street's centerline. Upon studying American culture and what is important to it, future anthropologists might take the Manhattan alignments to be cosmic signs of Memorial Day and, of course, baseball's All-Star break. If the Manhattan grid matched the geographic north-south line, then our special days would be the equinoxes, the two days on the calendar when the Sun rises due east and sets due west. But Manhattan is rotated 30 degrees east from geographic north, shifting the special days elsewhere in the calendar.”
(Link)
Then I remembered that Charles Petzold, author of the venerable Programming Windows series of books, came up with a precise measurement of the angle that Manhattan is tilted. He came up with something very close to 30°, or precisely 28.911°.