Old New-Gate Prison & Copper Mine
A colonial copper mine later used as Connecticut's first state prison, with underground workings and surviving prison ruins.
DocumentedTicketedFee or pass1 to 2 hoursChecked July 2026
Field files
The complete index.
66 sourced field files across all 50 states. History, folklore, and access rules are labeled on every record. The Atlas is curated, not exhaustive.
6 of 66 field files.
Strataca
A museum 650 feet below ground inside a working salt deposit, reached by a controlled mine descent.
DocumentedTicketedTicketed2 to 3 hoursChecked July 2026Mammoth Cave
The world's longest known cave system, with human history, enormous passages, and routes ranging from accessible to demanding.
DocumentedGuided onlyTicketed2 hours to full dayChecked July 2026Soudan Underground Mine
Minnesota's oldest iron mine, interpreted through seasonal underground tours and surface mining history.
DocumentedSeasonalFee or pass2 to 3 hoursChecked July 2026Pendleton Underground
A guided route through spaces beneath downtown Pendleton, presented by a nonprofit tour organization founded in 1989.
History + folkloreReservation requiredTicketedAbout 90 minutesChecked July 2026Seattle Underground
Buried storefronts and sidewalks left below Pioneer Square after Seattle rebuilt above its old street level following the Great Fire of 1889.
DocumentedGuided onlyTicketed75 minutesChecked July 2026