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 Theif movie
Percy and the questing group enter the underworld via the hollywood sign, On one letter is Ancient Greek writing. When Percy speaks what is on the letter, a bit of a hill next to the sign crumbles away, leaving an entrance to the Underworld, where Charon awaits them