Hollywood Sign

The Hollywood Sign in Los Angeles is the entrance to the Underworld in the movie version of Percy Jackson and The Lightning Thief.

The Lightning Thief
Percy and his friends enter the Underworld via the Hollywood Sign, following the map given by Luke. On the letter "H" of Hollywood, there was an Ancient Greek text. When Percy reads the text aloud, a bit of the ground next to the sign crumbles away, leaving an entrance to the Underworld, more specifically, the entrance at the River Styx where Charon (credited as "The Ferryman") awaits them.