Watch Tower on <a href="https://en.wikipedia.org/wiki/Alcatraz_Island" class="extiw" title="en:Alcatraz Island">Alcatraz Island</a> (San Francisco Bay, 2009). Alcatraz Island served as a light house, hosted a U.S. Army military installation, a military prison, and then (and probably most famously) as a United States Federal Penitentiary <a href="https://en.wikipedia.org/wiki/Alcatraz_Federal_Penitentiary" class="extiw" title="en:Alcatraz Federal Penitentiary">U.S.P. Alcatraz</a>.
<a href="//commons.wikimedia.org/wiki/User:Godot13" title="User:Godot13">Godot13</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>