This is one of the hottest tickets in Rome, for those who appreciate Roman antiquities and ancient Roman history. Nero's Golden House (or Domus Aurea) is open for guided visits on Saturdays and Sundays now through August 30, 2015. It's underneath the Colle Oppio park, just northeast of the Colosseum. The Domus Aurea had a huge influence on Michelangelo and his contemporaries when it was discovered during the early Renaissance. Anyone wanting to see it had to be lowered in by rope through a hole in the roof. The frescos and other decorations they found inside were then used by the artists in their own work.
More info here: http://www.coopculture.it/events.cfm?id=268
Look on that site for "How to Buy" to book a tour in English, Italian or Spanish. All visits must be done through a guided tour, and groups are limited in size to about 25.