From an email:

“Visitors to the Smithsonian can now play a smart phone scavenger hunt that will take them on a “Trek” through nine Smithsonian museums, decoding clues along the way. The game can be played for free from any smart phone by downloading the “SCVNGR” application from the iPhone App Store or Android Market. The game runs through July 24. At the end of the game, two winners will receive an Apple iPad.

BUT… if you are in town tomorrow, Saturday, June 26, we are also hosting a one-day only contest. Meet at the Smithsonian Castle Commons at 9:30 am to register and at 2 pm, the first-place winner will receive an iPad!”