What Is There To Do In Cinque Terre?
Hiking, swimming, snorkeling and just hanging out are the main attractions. I recommend taking the local train to Monterosso and walking to the next two or three towns.
The hike is steep and rugged at first but gets better as you get past town #3. The walk from Manarola (#4) to Riomaggiore (#5) is really easy. There are daily boat trips from Monterosso along the coast, stopping at some of the villages. Make sure you catch it before the last one of the day leaves. Even if you miss it you can still take the train back.
Take the boat all the way to Portovenere and get the bus to La Spezia. Day trips to Pisa, Florence and Genoa are possible. Try to stay two nights so as to have one uninterrupted day. There is also a scuba diving operation in Riomaggiore.
My overall description of Cinque Terre: Vertical towns. Expect a cardiovascular workout; this is not a town for people who spend all their time in a car or on the sofa. The Cinque Terre tourist office is in Monterosso al Mare, in Piazza Colombo.