Crypto Museum
cryptomuseum.comNeat. There is also https://www.nsa.gov/about/cryptologic_heritage/museum/ which I've been to, and recommend people check out if they're ever in the area, though the hours suck.
Seconded. It's just outside Ft. Meade. They have an Enigma machine (a small device) and the "Bombe" (much larger) that decoded it.
https://www.nsa.gov/about/photo_gallery/index.shtml#machines