Head out to any of the beaches at low tide, especially during the months of February, March and April, and you might return back to your hotel room with sand dollars, whelks or even a conch shell. (Actually, taking live shells is strictly prohibited.) The beach will whet your appetite for the Bailey-Matthews Shell Museum, the only museum in the country dedicated to shells. The highlight of the exhibition there is a revolving planet, with displays of shells from around the world. There’s also an exhibit on shell art, a detailed account on why so many shells wash up on Sanibel and a large collection of snails. The annual Shell Fair is held the first Thursday through Sunday in March, and it includes a shell art show