Infiltration
Recreation, Outdoors, Speleology, Urban Speleology - Infiltration. Website on urban exploration, featuring a webring, dictionary, and many pointers.
http://www.infiltration.org
Dark Passage
Recreation, Outdoors, Speleology, Urban Speleology - Dark Passage. A New York based organization providing blind archaeologists with the finest quality flashlights.
http://www.darkpassage.com
Welcome to Nettleden.com - a place for explorers
An urban exploration social network and reference site. The website with an interest in anything secret. Secret underground cities, classified military instilations, cold war nuclear bunkers, WW2 secret underground ammunition stores and underground factories.
http://www.nettleden.com/