It’s much like other augmented reality apps you may have seen for smartphones in that it uses a combination of the compass and screen to give you a heads up display of sorts. This allows you to see landmarks, restaurants, hotels, shops and public transport stations in your immediate vicinity simply by holding your phone up and panning around. As you’d expect you can filter based on the stuff you’re interested in and it’s has a Metro style interface.
If you’re on your desktop browser you need to transfer the link to your phone to install the app. If you’re browsing this page on your Nokia Lumia phone, you can install Nokia City Lens from the Windows Phone Marketplace. (Note: opening the Marketplace link on a desktop browser will give the error “App not found”.)
Final note: this app doesn’t work on the Nokia Lumia 610 as that device has no compass