horseshoe curve - Robuta Search

https://www.trains.com/ctt/videos-photos/videos/layouts/layout-visits/video-extra-the-pittsburgh-industrial-rr-horseshoe-curve/

A video of Nick Futules' layout

https://www.trains.com/ctr/railroads/railroad-operations/horseshoe-curve/

Horseshoe Curve is a 170-year-old engineering marvel that attracts millions to this day