The Hoosac Tunnel
The Hoosac Tunnel has been called a feat of engineering, excavating 2 million tons of rock in a straight line. Digging it out led to fatal accidents, and an exhibit tells the history of its making at the Western Gateway Heritage State Park on Route 8 just south of downtown North Adams. It took almost 25 years, and when it was built it was the second-longest in the world (after the French Alps)
It is still the longest active transportation tunnel east of the Rocky Mountains. The North Adams end lies on the east side of town, south of Windsor Lake and Historic Valley Park, and the historic trains do not run through the tunnel, because it is an active freight line — and 15 minutes of total darkness.