Centralia, Pennsylvania

Damned Interesting has a great introductory post on the town of Centralia, under which the very Earth is burning.

There is a small town in Pennsylvania called Ashland where Route 61's northbound traffic is temporarily branched onto a short detour. Exactly what the detour is circumventing is not immediately clear to travelers, however few passers-by pay it any mind... a detour is nothing unusual. But anyone who ignores the detour and ventures along the original route 61 highway will soon encounter an abrupt and unexplained road closure. Beyond it lies a town filled with overgrown streets, smoldering earth, and ominous warning signs. It is the remains of the borough of Centralia.