Super Spy Headquarters
From the Super Mario Wiki
In The Super Mario Bros. Super Show! episode "On Her Majesty's Sewer Service", Super Spy Headquarters was visited when Princess Toadstool secretly recruited Mario and Luigi as spies due to the fact that Secret Agent James Blonde was turned to stone by Koopfinger.
The only known entrance to Super Spy Headquarters is by pulling on a particular candle holder on a table in an Italian restaurant located in Spy Land. Once pulled, the table will descend down a deep shaft leading to Super Spy Headquarters, taking anyone sitting down with it.
Super Spy Headquarters is very high-tech in appearance. However, all that was seen of the place was the Super Spy Laboratory, where numerous spy tools and gadgets were located, including the Spymobile.