infiltration.org This isn't about corporate espionage but rather sightseeing in "places you're not supposed to go." One of the myriad subcultures exposing themselves to the rest of the world via the Internet is all about urban archaeology: crawling around slimy drain pipes, forgotten subway tunnels and abandoned buildings. Infiltration is out of Toronto and therefore somewhat Ontario-centric, but the articles will provide a good education for anyone who's ever wondered why he keeps buying all those Lonely Planet guidebooks.
www.bhere.com/ruins/ Among urban adventure cultists, The Fabulous Ruins of Detroit is considered one of the best sites devoted to the more-than-curious tourist. The photos on these pages have even gained a cult following of an altogether different sort. Seems some of the large, abandoned buildings it has spotlighted have drawn the eyes of rave organizers, and there's a section devoted to Detroit techno parties pumping some life back into these ghost dwellings.
home.att.net/~lakata/arch/ A lot of text and a few pictures chronicle visits to structures that at one time helped the San Francisco Bay Area grow up but have since been discarded. Take a look at the last whaling pier in the United States, a mining tunnel under the campus of UC Berkeley and a nearby ghost town.