Ilhéu da Cal

The highest of the six islets (179 m), off Ponta da Calheta and some 500 m from the shore. Its name comes from lime: its reef limestones — fossil corals 15.2 million years old, carbonate deposits and undersea volcanic rocks 12 to 16 million years old, capped by dune sandstones — were tunnelled with galleries to make lime, an industry that employed a good part of the population in the 19th century; the galleries can be seen from Calheta beach. Geosite, Natura 2000 site PTPOR0001, marine core of the Biosphere Reserve and of the Marine Protected Areas Network: Cory's shearwaters, Bulwer's petrels and storm petrels nest here, and the LIFE project (2010–2015) eradicated its mice. A no-entry zone: landing requires IFCN authorisation; admire it from the sea, by kayak or boat from Ponta da Calheta, where a large cave opens in its flanks.