Paestum is a really old town in Italy that people used to live in a long, long time ago, when dinosaurs still roamed the earth (not really, but a very long time ago). The town has lots of giant buildings that are made out of rocks, and people can go and see them now, even though they're really, really old.
Paestum is special because it has some really big buildings called temples, which are like special houses where people used to go to worship their gods. These temples are so big that they might seem scary, but they're really cool to look at.
People who go to visit Paestum can walk around and look at the temples and imagine what life was like for people who lived there a long time ago. It's kind of like going back in time!