It became a military jail in the 1870s, but it wasn't until it was converted into a high-security federal penitentiary in 1934 that the name Alcatraz became an international symbol of punishment.

Despite being in operation for less than 30 years, Alcatraz remains fixed in the popular imagination as the ultimate penal colony. (As do some of its inmates.)

Today, its ominous prison buildings are no longer used (its last inmates left in 1963), but the craggy outcrop, now a National Park, lures well over a million visitors each year.

Despite what you might expect, Alcatraz is far from being from a tourist trap. The audio tour of the facility, which features insights from a variety of former prisoners and guards, is wonderfully effective, and the buildings retain an eerie and fascinating appeal.

Departure times for both the day tours and the far less frequent (and wildly oversubscribed) evening jaunts vary by season: check the website for details. One word of warning: capacity on the tours is limited, and those who don't book ahead of time may find the only views they get of the island are from the shore.