17. Oheka Castle

Photo: Peter Kramer/HBO

The annual corporate retreat for the board of Waystar Royco supposedly takes place in Hungary, but is actually filmed at Oheka Castle in Cold Spring Harbor on Long Island. The Gilded Age mansion of Otto Kahn, now often used for weddings, the 127-room estate is the second-largest private house in the United States. During the heydays of the Gold Coast of Long Island during the 1920s, Kahn used the lavish estate to host extravagant parties and entertain royalty, heads of state, and Hollywood stars.

Next, check out the filming locations for Billions on Showtime.