The land this country now occupies used to be a cemetery later covered by the Circus of Nero.
A 1932 addition to a museum in this country was the inspiration for Frank Lloyd Wright's Guggenheim, which adapted the black, double-helical staircase designed by Giuseppe Momo. That staircase here was itself based on a spiral ramp designed to allow horseback access to the upper levels of the Belvedere Palace. This country's most modern building is an [*] audience hall whose gently undulating roof is now covered by solar panels. The land this country now occupies used to be a cemetery later covered by the Circus of Nero. This country is home to a basilica worked on by Sangallo, Maderno, Bernini, and Michelangelo. For 10 points, name this country that is home to the Paul VI Audience Hall and St. Peter's Basilica. 
A 1932 addition to a museum in this country was the inspiration for Frank Lloyd Wright's Guggenheim, which adapted the black, double-helical staircase designed by Giuseppe Momo.
Vatican City State [or Stato della CittÃ  del Vaticano]