To the south of the Cape, the warm waters of Nantucket Sound play host to families with kids and the younger adults who gather at Craigville Beach in Centerville and along the Falmouth Heights Beach. The relatively shallow waters, which only reach about 40 feet at their deepest spots, heat from the summer sun. In the height of the summer, average temperatures at the beaches on the south side in Nantucket Sound reach the high 60s and mid-70s.