The ceiling.
The room itself, with the Apollo fragment in the middle of the image.
The tour continues into the Round Room which holds a monolothic porphyry basin, over 4 metres in diameter!
And there's another dome.
And more amazing statues.
The major attraction in this room is the two porphyry sarcophagii. This is the one for St. Helen, the mother of the Emperor Constantine. The other (decorated differently) is for the emperor's daughter.