Door of Orpheus

The Door of Orpheus is an entrance to the Underworld. It is located in New York City, more accurately, in the southern area of Central Park. It was created by Orpheus to get his wife back. He created it by using his skills in music and opened the path straight into the Underworld.

The Last Olympian
Nico and Percy use the Door to enter the Underworld, so Percy could bathe in the River Styx. They needed help from Grover, who played his pipes (a Nirvana tune) to open a tunnel in the rocks big enough for Nico and Percy to crawl through. This is due to the fact that Orpheus created it with his music.