Fontana dell'Acqua Paola in Trastevere, Rome

Here's information about the fountain on Rome's official tourism website:

https://www.turismoroma.it/en/node/1281

As it states, you can view the front of the fountain for free; the garden behind requires a reservation for groups or individuals. It includes a link for accessing that info, which is in Italian; just use a translation tool.

No tickets are required to admire the Fontana dell'Acqua Paola (the Fontanone) on the Janiculum Hill in Rome. The front area is always accessible to the public.
For access to the rear garden as an individual (paying ticket), a reservation is required, contacting 060608, and according to a schedule.
Schedule and other information here http://www.sovraintendenzaroma.it/content/modalit%C3%A0-di-accesso-e-prenotazione-ai-monumenti-del-territorio

Yes, that reservation-info link was included in the tourism website I'd provided.

Note that there are actually two Fontana dell'Acqua Paola in Trastevere.
The one called Fontanone del Gianicolo is the one from the famous scene in The Great Beauty. Directly below it, on the banks of the Tiber, lies the second, the Fontanone di Ponte Sisto.
This latter was originally located on the other side of the Tiber, where the Via Giulia ended.
An aqueduct brought the water to the Gianicolo, from where it flowed down, supplying Rome with water via pipes under the Ponte Sisto to the Fontanone di Ponte Sisto) (originally named Fontanone dei Cento Preti). In 1879, this fountain was dismantled for the works on the banks of the Tiber, only to be rebuilt 20 years later in its current location at Piazza Trilussa (although only half of the stones were recovered, justifying the smaller version).
https://www.turismoroma.it/en/places/fontana-dellacqua-paola

Thanks everyone, much appreciated for all the replies!

tcgnj, just curious? As there apparently are 2 fountains of similar name, which one were you asking about?

Kate,

The one near the Tempietto -- https://www.sovraintendenzaroma.it/i_luoghi/roma_medioevale_e_moderna/fontane/mostra_dell_acqua_paola_al_gianicolo
I guess it is called the Fontanone del Gianicolo.
Thanks