SAN FRANCISCO - JULY 2: Visitors tour the mail cell block of the Alcatraz Federal Penitentiary on Alcatraz Island July 2, 2003 in the San Francisco Bay, California. The National Park Service, which manages Alcatraz as one of San Francisco's most popular tourist attractions, has started selling boxed chunks of concrete rubble for $4.95 which were left over from a 7.7 million dollar retrofit of a decaying cell block and guards quarters. Park staff came up with the idea as a cost-effective alternative to ferrying tons of rubble off Alcatraz and to bring in an extra $20,000 to $40,000 a year. (Photo by Justin Sullivan/Getty Images)