It's almost criminal that something so beautiful could fall into disuse, but it has. The person you see in the picture is breaking the law; nobody has been allowed to cross the Devil's Bridge in Rakotzbrucke, Germany, for years.
The law has been put there to protect this strangely beautiful feature. The bridge is delicate, and crumbling away. One day it will fall into the water below it, thus ending the optical illusion of a perfect circle that it creates.