Past the shell museum the island thins and quietens. This is the better half for shelling, for the simple reason that the access is harder.
Bowman's Beach is the island's best-known shelling beach and the least convenient, which are related facts. You park, then walk a footbridge over a tidal creek and a few hundred metres of path to reach the sand. That walk filters out a meaningful share of casual visitors, and the wrack line shows it. Facilities are basic and the parking is metered like everywhere else.
Gulfside City Park, sometimes still called Algiers Beach, sits further east off Algiers Lane: smaller, quieter, backed by Australian pine stumps and sea grape, with a short walk in and a reputation among residents rather than visitors.
Tarpon Bay Beach is the mid-island Gulf access at the end of Tarpon Bay Road, the one most people can actually find, and correspondingly busier.
Blind Pass is where Sanibel ends and Captiva begins. The pass is a working tidal cut and it moves; it has shoaled closed and been dredged open more than once in living memory. The beach either side of the bridge collects shell heavily because the current sorts it there. It is also genuinely hazardous for swimming near the bridge, where the water deepens fast and the flow through the pass runs hard. Fish the jetty, shell the beach, swim somewhere else.
Turner Beach, on the Captiva side of the bridge, is Lee County rather than City of Sanibel: open 24 hours, parking around $5 an hour paid by phone, ADA-accessible restrooms, and no dogs — the Captiva rule, which catches out visitors who walked one over from Sanibel.