The Temple can be visited
Tempio dei Dioscuri (Temple of Castor and Pollux)

The Tempio dei Dioscuri, also known as Aedes Castoris, is an ancient temple located in the Roman Forum in Rome, Italy. Dedicated to the twin gods Castor and Pollux, it is one of the oldest sacred buildings in the Forum, with a history dating back to the early Roman Republic.
History+
The temple is said to have been vowed in 499 BC after the Battle of Lake Regillus and consecrated in 484 BC, as the Dioscuri were believed to have helped the Romans achieve victory. In 117 BC, the structure was renovated by Lucius Caecilius Metellus Delmaticus.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:RomaForoRomanoTempioCastori.jpg
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 41.8917, 12.4858