Well yes, not strictly speaking Tuscany (Liguria, actually), but so many visitors to Tuscany have the Cinque Terre on their 'must-see' list that we thought we'd include 'it', particularly as the starting off point for the trip is so often a train/boat from Viareggio/La Spezia. Scroll down for some more information and links to numerous photographs.
The Cinque Terre are five small fishing villages that lie down the coast from Portofino; they all cling to the sides and tops of the steep coastline and were only reachable by boat until well into the 1960's. There are numerous trails that cover the 15 miles between villages (Monterosso, Vernazza, Corniglia, Manarola and Riomaggiore), but be advised that these are hikes as opposed to strolls, winding down to the coast and back up into the forests.
Nowadays there is a rail line connecting the five villages that blasts its way through the cliffs, occasionally opening up into galleries that offer tantalising glimpses of the impossibly blue water below. Catch the train from La Spezia or Genoa, or for a far more traditional and gentle visit, take one of the numerous water ferries that run from La Spezia and Portovenere. You may also take a ferry that starts out further south in Viareggio, but you'll need to get there early in the morning.