The Cascata delle Marmore or Marmore Falls is a man-made waterfall created by the ancient Romans. Its total height is 165 m (541 feet), making it the tallest man-made waterfall in the world. Of its 3 sections, the top one is the tallest, at 83 m (272 feet).
It is located 7.7 km from Terni, a provincial capital of the Italian region of Umbria. Its source is a portion of the waters of the river Velino (the rest of the river flows into a hydroelectric power plant), after flowing through Piediluco lake near the community of Marmore.
It pours into the valley below formed by the river Nera. Its flow is turned on and off according to a published schedule, to satisfy the needs of tourists and the power company alike. Tourists try to be there the moment the gates are opened to see the powerful rush of water.
Normally, the falls are turned on between 12:00 and 13:00 and again between 16:00 and 17:00 every day, with additional times on holidays.
A path along the falls allows the visitor to hike up to the top of the falls. Along the way, a tunnel leads to an observatory just next to the falls, where a visitor is guaranteed to get soaked.
A safer observatory near the top affords a grandiose view of the falls and of the Nera valley below.
According to en.wikipedia