Fort Hard Knox

Fort Hard Knox is the piggy bank-shaped treasury of Spy Land.

In The Super Mario Bros. Super Show! episode "On Her Majesty's Sewer Service / 9001: A Mario Odyssey", Koopfinger and his goons robbed Fort Hard Knox, and managed to make off with nine-hundred and ninety-nine billion trillion billion million and one Gold Coins.

Other than a gate, Fort Hard Knox has no visible security, which might explain why it was so easy for Koopfinger to plunder.

Trivia

 * Fort Hard Knox gets its name from "Fort Knox", a similar fortress made to hold money, and the idiom "School of Hard Knocks", a term used to describe the simple education given by mere life.