 The early port settlement of Plymouth , called " Sutton " , approximates to the area now referred to as the Barbican and has 100 listed buildings and the largest concentration of cobbled streets in Britain . The Pilgrim Fathers left for the New World in 1620 near the commemorative Mayflower Steps in Sutton Pool . Also on Sutton Pool is the National Marine Aquarium which displays 400 marine species and includes Britain 's deepest aquarium tank . 
