Along the east side of Piazza del Plebiscito is the former Royal Palace, begun in 1600 by Domenico Fontana and restored from 1837-41. It is one of four palaces in the area that were used as residences by the Bourbon kings. On the long facade are eight marble statues of the various kings who ruled Naples. Inside, you can see the grand staircase of white marble, built in 1651, a theater, and more than two dozen rooms in its state apartment, with furniture, tapestries, porcelains, and sculptures. It's rarely crowded, inexpensive, and you get a free audio tour. Many visitors consider this one of Naples' most interesting and under-sung attractions.
Connected to the palace is Teatro San Carlo, one of the largest theaters in Europe and one of Italy's premier opera houses. Along with its outstanding acoustics, San Carlo has the reputation of attracting the noisiest and worst-behaved audiences in Italy. Woe betides the tenor who misses his high C here.