The Cascata delle Marmore (Italian:) 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.

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. After flowing through Piediluco lake near the community of Marmore (italian), it pours into the valley below formed by the river Nera. The flow of the waterfall depends on an off and on scale with a published schedule to support the power company nearby.

Most of the time, the water in the canals above the Cascata delle Marmore falls is diverted to a hydroelectric power plant, so the flow in the falls themselves is heavily reduced. Piediluco Lake, above the falls, is used as a reservoir for the power plant. The Galleto power plant, built in 1929, is architecturally interesting. Its capacity is about 530 MW. To control the operation of the power plant, and to satisfy tourists, the falls are turned on according to a set schedule, achieving a spectacular effect at full flow. An alarm is sounded first, then the gates are opened, and in a few minutes the small stream is transformed into a full-sized river rushing into the void below.

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. An entrance fee is charged to visit the falls and the surrounding area.

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 likely to get soaked. Another observatory near the top affords a wide view of the falls and of the Nera valley below.
Without quoting directly from the text give me a summary of how turist visit the falls even if they are used for hydroelectric power production.
The Marmore Falls are used as a hydroelectric power plant, but to allow people to enjoy the spectacular water flow, the gates are periodically opened to present the full-sized river rushing into the void. 

The tourists can visit the falls on a fixed schedule (12:00 to 13:00, 16:00 to 17:00 plus additional times on holidays) following paths that allow them to reach the top of the falls.