Open Street Map
Open Street Map is an open source map of the world, created and amended by people all over the planet. It emphasizes local knowledge, so if you're in a city and know of a new route or location, you can feel free to add it. There are many types of contributors, from mapping enthusiasts, to professionals, to humanitarians that help add things during disasters. The map shown here was listed as a great example of a community-made map of Pompeii, Italy.
Image: Open Street Map