Segovia

 Segovia is famous for its very well preserved, Roman aqueduct.  It still works - but I think they have discovered pipes.

The Romans had to find a water source, figure out the lie of the land, and build a channel to where they wanted the water, sometimes building a bridge underneath.  No computers - just engineers, a plumb bob and slaves.

The aqueduct is visible from outside town.

More pics. 

We were told that there was no mortar involved in building this aqueduct.  Just stones fitted together properly.  Wonder how many tries they had to make? Or how many slaves were harmed in the making of this bridge!