The Pont du Gard is a famous Roman aqueduct crossing the river Gard or Gardon close to the city Vers-Pont-du-Gard, France. It is an impressive building from the 1st century CE and was part of a 50 kilometers long system transporting water to the city of Nîmes. It is 49 meters high and is surrounded by a very good touristic infrastructure.
When I was a teenager it was still possible to walk on top of the Pont du Gard and I remember this as pretty dangerous. Today this is only possible within a guided tour and you can only walk on the lower level at a height of 22 meters. In addition you can walk to the upper end points of the aqueduct and follow the water trails.
400 Route du Pont du Gard