We all lose things -- keys, wallets, patience -- but how do you lose an entire city? Hear the stories of three American towns built in a hurry but kept off the map, secure Soviet enclaves known by their post codes, ancient cities found by modern technology, and the ingenious engineering of underground dwellings.

Reach out and touch Moxie on Facebook, Twitter, or Instagram.

Music by Kevin MacLeod.

Links to all the research resources are on our website.

Learn more about your ad choices. Visit megaphone.fm/adchoices