I have already published a post titled "River Harp" where a part of a big metallic sphere is visible (related post). Here is a video featuring that sphere, namely the "River Harp", so you can hear its sound.
Being more precise, there are two such spheres, one on each river's bank. This is in Drammen city, Norway. The sound that these spheres produce are made of harmonies that are sung by a local choir. The sound generation is dependent on the surrounding condition all collected by a nearby bridge and send to the spheres. The bridge is called Ypsilon where surrounding condition such as the river current, pedestrians walking over the bridge, wind, cars passing nearby, etc., induce some vibrations on the bridge. Then the vibration is somehow transferred to the spheres and they are translated to sound harmonies. Neat!
Here is a photo where you can see the Ypsilon bridge and one of the River Harps (look for a shiny metallic sphere about the middle of the photo).
And here is the video:
p.s. This reference helped me to better understand River Harps: reference.