A walk through the historic city center, under the streets of Seattle.

"The House That Love Built" is shying away from "The House That Ghosts Love."

A frozen relic of Seattle's hydroelectric boom is now a teaching facility for future engineers.

During its heyday, 72 one-ton buckets from this dredge bore into the Powder River excavating vast gold deposits.

The steepest tramway in North America provides stunning views of the out-of-the-way Wallowa Mountains in northeastern Oregon.

Train debris from the deadliest avalanche in United States history can still be found in the ravine where so many perished.

The site of the Wellington avalanche, one of the America's worst railroad disasters.

This long, dark tunnel is open to hikers, but those without lights are known to get confused even on the straight path.

The Bucyrus-Erie model 1850B electric shovel, or "Big Brutus," the largest existing electric shovel in the world.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.