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", Koopfinger and his goons robbed Fort Hard Knox, and managed to make off with nine-hundred and ninety-nine zillion 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.