It's the needle dam along the Reuss River. You'll recognize and hear it right away when walking up the south side of the river on the pedestrian path known as the Reusssteg on your way to the Spreuer Bridge.
It's not as impressive as the more modern day dams, but it's very unique. This one was built back in the 19th century to control the flow of water. It's uses thin slats of wood to regulate the water level and can be adjusted by adding more wood. It's just cool to see it in action and upclose as you walk by it.
There are very few operational needle dams that exist today. You might as well see it while you're there. read more