Tōmyōdō Coast, Yokosuka

What Seaglassmap found here

Kantō's worst-kept secret. The main beach under the Tōmyōdō lighthouse is picked over and can leave you with nothing but pottery. The glass is in the small cove one rock scramble further south, barely bigger than a room, and it fills with bigger pieces than the main strand. Come at low tide, because the cove all but vanishes at high water, and wear shoes: red jellyfish wash up here. Buses run from Kurihama; there is paid parking by the lighthouse.