I found this to be an interesting use for QR Codes. It is a map of Rome with the codes set on specific, most likely touristy locations. You can find a detailed image of the painting here. Each QR Code, in this instance, links to a Wikipedia article. This is located at Galleria d’Arte Moderna in Palermo, Italy.
While this is a great use of the technology, it’d be much more immersive if it linked to video as well as the wiki content. One of the great things about being able to connect real-world locations to mobile content is that you aren’t limited just text and static imagery.