COLOSSEUM
I visited Rome when I was on the Amalfi Coast. It is ca. 4 hours by bus. I bought this Colosseum guided tour that lasted just one afternoon, but it was worth it for sure.
It was special being there and feeling impressed by its architecture and history. The biggest Roman amphitheater ever constructed has a seating capacity of 75,000 people. It was built over ten years (70–80 A.D.) and for five hundred years hosted gladiator fights, animal hunts, and shows. During its inauguration, nine thousand animals were killed. Apart from the Colosseum, you still have monuments and preserved ancient sites to visit there.