In its heyday in the 18th and early 19th century, Naples was one of the most important cities in Europe, and the dimensions and splendor of the Royal Palace are reminders of that era. You can visit the lavish Royal Apartments (accessed via a monumental marble staircase), the magnificent red-and-gold Court Theater, the ornate Palantine Chapel and the massive Biblioteca Nazionale, which houses an important collection of books and manuscripts, some of them dating from the 5th century.