Paestum is 30 min. from Salerno by train.
It' very nice place to see ancents monument of 5 century B.C. but I advice you to go in daytime, to get ruins you has to take a walk 30 min. from railway station in a cornfild, it's quite scary after sun set. Near the station you can find nothing, nobady to ask help, pleace visit in the morning if you visit by pubblic transport.
Few train stops Paestum station, you need check timetable before and don't belive any information of the local people, they don't know nothing about pubblic transport, they wanna just take a time with you.
There are two bus stops (at the Paestum end) that connect Salerno to Paestum. One of these bus stops is just outside the site on the Temple of Ceres end, near a gift shop and tabacconist. This bus stop is clearly marked with a bus shelter, sign and benches. Plus, you can buy your return tickets at the tabacconist. I highly suggest you use this bus stop when returning to Salerno!
Unfortunately, I waited at the other bus stop, which is across from the restaurant at the two-temple end. There is a bus stop on one side of the road that is marked, but the stop for busses going to Salerno is beside an agricultural building, unmarked. As cars stop at the nearby traffic lights, traffic backs up and you end up providing entertainment for bored drivers. In thirty minutes I had TWELVE men pull over to the side of the road and try to convince me to get into their cars. Some thought I was a prostitute, others offered me rides back to Salerno, and some went so far as to wave their wallets at me. There isn't much foot traffic at this place, so you're really quite isolated. I was extremely fearful for my safety, but didn't know there was another bus stop. The worst part was when I was "attacked" by two small lizards and one tried to crawl up the leg of my pants! I don't know where they came from, but suddenly I heard and sound and the next thing I knew I could feel reptile on my ankle! I was so afraid that I would have to take off my pants to get the lizard off me (thus making myself look even more like a prostitute!).