The Temple of Diana Nemorensis was part of an ancient Italic monumental sanctuary erected around 300 BC and dedicated to the goddess Diana. It was a popular place of worship until the late imperial age.
The temple was situated on the northern shore of Lake Nemi, beneath the rim of the crater and the modern city of Nemi.
Wikipedia https://en.wikipedia.org/wiki/Temple_of_Diana_(Nemi)
Address 00040, Italy
Coordinates 41°43'26.893" N 12°42'34.851" E