This park was born out of a work of hydraulic engineering. The Aniene flooded Tivoli constantly, and after a disastrous flood the pope had two tunnels dug through the mountain to divert the river: the water came out on the other side forming a waterfall a hundred and twenty metres high, and the old riverbed, left dry, was turned into a garden in 1835.
What to see
You go down into the gorge by paths and stairways, with the vegetation changing as you descend and the heat of the entrance square giving way to the damp of the bottom. Down there are the caves cut by the water, the grotto of Neptune and that of the Sirens, and the points from which the great waterfall is seen at different heights.
On the opposite ridge stand the two Roman temples, the round one and the rectangular one, which Grand Tour travellers painted thousands of times. The park was abandoned for decades in the twentieth century, then restored and reopened in 2005: the paths are the historic ones, made safe again.
Visiting
The entrance is in Tivoli, in largo Sant'Angelo, forty minutes from Rome by train or bus; paid ticket, with seasonal opening and winter closing. Two hours. The route is all up and down, so proper shoes are needed.
Our editors' tip
Go right down to the bottom of the gorge even if the climb back frightens you: that is where you understand what happened here, because you stand inside the canyon with the walls above your head and the water thundering. And remember that this landscape, so natural-looking, is the result of a decision taken in an office, to stop the town from flooding again.