After having renovated the area of the high altar with the baldachin, Bernini placed the spectacular Chair of Saint Peter at the end of the basilica's long, central viewpoint. The "chair" is the ancient wood and ivory throne that you can see surrounded by rejoicing saints and angels. A symbol of the Pope's authority, the chair seems to be suspended in mid-air, held up by the statues of the four Doctors of the Church. Notice also the dove in the middle of the oval window above it: this is the symbol of the Holy Spirit, set among clouds, angels, and rays of stucco and golden bronze.
But that's not all: Bernini created two more scenographic sculptures for the basilica. The first is in the atrium and is the statue of Emperor Constantine, and in the left transverse arm you can see the Tomb of Pope Alexander VII. In this last work Bernini once again took advantage of the effect different colors and materials can create, bending the red marble to simulate the folds of rich fabric.
Bernini was helped by numerous assistants in all the works for San Pietro: the construction site was practically a style gym where all the main sculptors and architects of the Roman Baroque period "worked out".
Your tour of the basilica continues with the Tesoro, or Treasure, near the sacristy, where you can admire liturgical objects, historical memorabilia, and artwork. It's probably not as rich a treasure as you'd expect, but keep in mind that the German mercenary soldiers took it all in the famous invasion of Rome in 1527. I'd like to point out two sculpture masterpieces that were made over a thousand years apart: the Sarcophagus of Giunio Basso in marble from the 4th century AD with scenes of Christ's life, and the Tomb of Sixtus IV (the pope who had the Sistine Chapel built) in gilded bronze, by Antonio del Pollaiolo.
Lastly, under the central nave of St. Peter's you can visit the Vatican Caves, where you can admire the site of Saint Peter's martyrdom, the remains of the early Christian basilica, and various popes' sarcophagi, including John Paul II.
FUN FACT: a popular belief says that there's a secret way to become rich in St. Peter's Square. Go to Bernini's colonnade and look for the column that a German signed with his name many years ago. Touch this signature and go straight to playing the lottery, using the month, day, and year of your birthday. Try it, you'll definitely win!