The city of Haarlem wanted to create a safer situation where a main road crossed another main road coming off a bridge.
For some reason all practical solutions turned out impossible (more likely someone couldn’t be bothered) so the city opted for a work-around, albeit a well designed one. They built a bicycle bridge that wraps around the underside of the other bridge and then partially submerged the bicycle bridge. The result is either a submerged bridge or an open air tunnel, your pick.
The bridge was designed by IPV who seem to be specializing in these sort of crazy work-arounds—check their bicycle roundabout hovering above Eindhoven.
Mark Wagenbuur, the bicycle vlogger, visited Haarlem and shot one of his trademark videos there.