Wrapping up this one:

Aapravasi Ghat
Camino Real
Canal du Midi
Chhatrapati Shivaji Terminus
Forth Bridge
Grand Canal - best of the canal sites, and an impressive feat of engineering
Grimeton radio station - we have to show the Little Green Man how we started "communicating" wirelessly!
Goree
Kunta Kinteh
La Lonja de la Seda
Frankincense
Mt railways of India - quirkiness
Pontcysyllte
Qhapaq Nan - Inca road system
Rhaetian Railway
Rideau
Semmering
Silk Road - trade route that significantly shaped history between Asia and Europe
Four Lifts
Vizcaya