Central Park is public park in Manhattan, New York. It has an entrance into the Underworld.
DOORS TO THE UNDERWORLD
(please go to the "Tatarus/Underworld forum when you have entered HELL)
Door of Orpheus
The Door of Orpheus is a lesser-known entrance, which stands in Central Park, NY. Orpheus created it to retrieve the dead spirit of his wife, Eurydice. Music is required to open this door. It lets out behind the main gates, therefore being more direct to Hades' palace.
The Doors of Death
The Doors of Death act as way for Thanatos to quickly enter and exit the Underworld. However, he claims that the doors aren't in a physical place and normally only he knows where they are. Unfortunately after Thanatos was captured, Gaea managed to use the Doors of Death to allow monsters to quickly reform and souls to return to the land of the living, such as Medea, King Midas, and Phineas.
Other Entrances/Exits to the Underworld
While the above entrances are the main ways to get into the Underworld, there are other ways to get out. Hades can use the his keys to create and close gates to the Underworld almost at will. The exact locations of these entrances are unknown.