• What to do: For centuries, traversing the Allegheny Mountains was a difficult, time-consuming and dangerous journey. In the 1850s the Pennsylvania Railroad hired civil engineer J. Edgar Thomson (the Braddock mill was named for him) to build the first rail route over the mountains. Solving a complex engineering challenge about five miles west of Altoona, Thomson built a long, inclined U-curve in the track spanning two mountains.

The juncture was so vital in transporting Pittsburgh industrial products to eastern ports, it was guarded by the Union during the Civil War and Nazi Germany launched a failed plan to sabotage it. The Curve is now a working National Historic Landmark. Much is explained at an informative visitor center museum.

See it for yourself on an incline and observation site.

• Contact: 814-946-0834, www.railroadcity.com/hc.