Shell collecting @ Shell Beach Sanibel Island, Florida. 15 miles of beaches, 22 miles of bike paths, abundant wildlife and the largest undeveloped mangrove ecosystem in the country. The island is actually made of shells. Sanibel fishing pier and lighthouse beach, one of the six public beaches on the island. You can bike to this beach on the Periwinkle pathway (you can see it on the map). Lighthouse beach, along with Blind Pass are the two top destinations for shelling.