A long sandy beach that is, um, clothing optional
Just north of Corniglia is the most famous of the coast's little beaches, Guvano. At an abandoned train station, walk through the spooky tunnel to the metal gate. Ring the bell and you'll be buzzed in by a guy who will want €5 ($6) to cross his property to get to the Cinque Terre's only nude beach.
Note #1: In the "fair warning" department, you should know that the nude beach is full mostly of naked men—men who are, for the most part, very happy that it's full of naked men. If this describes you, have a great time; if not, you might want to try a different beach.
Note #2: Deaths are rare on the Cinque Terre trails, but most of those that do occur happen right above Guvano, as would-be peeping Tomassos get a little too close to the edge and slip over on the loose gravel.