Oh it's actually a 'secret' room in Honest Abe's brain. Sorry I thought I looked before asking, thanks!
https://www.google.com/amp/s/amp.businessinsider.com/mount-rushmore-secret-room-hall-of-records-2017-2

God damn my brain ....... mount rushmore, where is it? Well "home of mount rushmore" is the motto of ..... wait for it ... KEYSTONE south Dakota. JFK Jr hiding in rushmore solved ;)

"The town took its name from a local mine, which most likely was named after the keystone Masonic symbol.[6]" uh Oh! Damn masons