No smoking.

So we all know the Incas built some pretty good rope bridges. As engineers period they are up there. Now they didn't get far with no wheels, but rope bridges they did OK. The largest of these spanned 200+ feet over the Apurimac Canyon.

The cool thing with these rope bridges including others built in South and Central America was the commitment to regular maintenance. Locals would rebuild and tighten main sections of the bridge on a fixed schedule, prolonging the useful life and keeping harmful accidents at a low level.

Far, far away in Northern Ireland, we see the bridge builders craft displayed in the Carrick-a-Rede Rope Bridge, near Ballintoy. This amazing little bridge actually spans the ocean between Ireland and tiny Carrick Island.

Area fisherman erected the bridge as an easier way to get their catch to land (thought they would have had boats though). This bridge shows up in local lore and seems to have been around off and on some 300 odd years. The current version is all safe and has safety measures installed so its pretty much for tourists. It's still a harrowing 20 metre walk on a shaky bridge.