http://wikipewt4n75trifcse2ggaieot27svognl7idu6xmmqn37kf64rvsyd.onion/index.php?title=Main_Page
Services can go down temporarily, so we keep track of when they do and maintain a list of dead hidden services. In addition to an onion simply being gone (Tor cannot resolve the onion), sites that display 404 (and use a known onion/URL based hosting service) are the only other thing that is considered truly DOWN.