18. Alcatraz | San Francisco, CA
This imposing structure in the middle of San Francisco Bay started as a lighthouse station in the 1870s and later transformed into a military prison. It gained notoriety as a maximum-security prison in 1934, housing some of the most infamous criminals of the early 20th century. Today, the island is accessible to the public via a ferry from Pier 33 Alcatraz Landing. A visit typically takes about three hours, during which you can explore its fascinating history. A self-guided audio cellhouse tour, narrated by former inmates and guards, delves into harrowing escape attempts, prison riots, and the 19-month-long occupation by Native Americans in 1969, demanding reparations for broken treaties.