Crazy Horse Memorial
Started in the 1940s as a one-man project, this museum memorial is still a work in progress, carving a mountain into a representation of Crazy Horse on his steed. (Crazy Horse never allowed his picture to be taken, so it is not his likeness.) The 'Carving a Mountain' section is informative on this uncommon medium.
dead link: http://www.crazyhorse.org/