One of Italy's most-visited attractions is, of course, the excavation of Pompeii, and within that ancient city the remains of the Temple of Apollo are a must-see. The site dates from roughly the 6th century BCE. It's one of the first structures visitors see upon entering the main part of Pompeii, as it sits to one side of the expansive forum, and it's the oldest religious structure at the site.
The temple was once surrounded by 48 columns, though only a few remain standing today. Two statues found in the excavation of the temple – one of Apollo and one of Diana – are in the excellent National Archaeological Museum in Naples, though replicas are now where the originals were found.
The Temple of Apollo is on the north side of the excavation on the ancient forum. Admission to Pompeii is €11 for adults, €5.50 for seniors or students ages 18-25. The site is open April-October 8:30am-7:30pm, November-March 8:30am-5:30pm.