Cha-ching! The nation's paper currency is designed and printed here. Guides lead 40-minute tours during which you peer down onto the work floor where millions of dollars roll off the presses and get cut (by guillotine!). In peak season (March to August), timed entry tickets are required. Get in line early at the ticket kiosk. It opens at 8am.
During non-peak season (September through February), no tickets are required and you can come in through the main entrance at 14th and C Sts; tours take place every 15 minutes from 9am to 10:45am and from 12:30pm to 2pm.