AudioGuide is a location-based travel app. It will find information from Wikipedia about all the nearby landmarks, sights and points of interest. And it can read the info to you through your headphones, while you are busy sightseeing.
Anywhere in the world.
For free.
AudioGuide requires internet connection to work, but it uses your mobile data sparingly as only the text of the articles is transmitted over the network. The voice synthesis is done on your phone.