Stuck on Earth is one of those 'really good ideas' that only seems obvious after you've seen it and spent some time with this free app.
It's designed for travelers and especially photographers. Move a map to any place on earth, and as you zoom in you will begin to see photographs taken at those locations. The photos come from Flickr and other sources, and the developers check those images by looking for embedded GPS coordinates so the photos appear at the right place on the map. Many of the photos have comments, and you can get directions to any of the locations from directly inside the app.
It's a great way to explore things that are near you that you've never seen, but also it's a really useful resource when you're on the roa