In case you've been holidaying on Mars and haven't yet discovered Google Earth, it is not a website in itself but a free application that's downloadable online. Working like a photographic map it lets you explore the world by zooming in and out of satellite images. What's that got to do with travel, beyond general curiosity? Well, it's a great research tool. Want to check how close your hotel is to the beach or see how private the pool really is? OpenGoogle Earth and you may well be able to find out, though there are still lots of gaps.
Like that? Try www.geograph.org.uk