peninsula in Kerrier district, administrative and historic county of Cornwall, England, the southernmost part of the island of Great Britain. The coastal scenery is magnificent, with offshore rocks, rugged cliffs 250 feet (75 metres) high, and small coves. Inland the landscape is level and open. The local serpentine rock is used for building. At Poldhu a monument marks the spot where in 1901 Marconi sent and received the first transatlantic radio message. There are several villages on the peninsula.