Santo Antão, or Sontonton in Cape Verdean Creole, is the second largest island of Cape Verde and westernmost point of Africa. The nearest main island is São Vicente to the southeast, separated by a channel named Canal de São Vicente.
The island is entirely made up of volcanic material. The tallest mountain is Topo de Coroa, reaching a height of 1,979 m. The second tallest is Pico da Cruz at 1,585 m.
The island is divided into north and south by a mountain range long considered impenetrable but now crossed by a road. The island’s main town is Ponta do Sol on the north coast, home to the closed Agostinho Neto Airport, while its ferry port is Porto Novo on the south coast. A part of the island in the southeast has an arid climate, while the northwest receives relatively normal precipitation. Its valleys are suffering heavy erosion.

Bathing beaches and fishing areas are found in near Tarrafal de Monte Trigo. During the rainy season, some creek beds across the island are temporarily filled with water.

The island is considered one of the most mountainous of Cape Verde. Its mountains are composed of basalt and many of its volcanoes are young, especially its calderas. Since 1999, vulcanologists have observed continuous rising of the water temperature of the sea in the area of Ponta do Sol which may indicate the risk of a new eruption in the area.

Being basically made of several stratovolcanoes and so extremely mountainous, this island has quite diverse climate and various microclimates due to its deep ravines.
The average annual temperature on the coast is about 23 °C, decreasing to somewhere between 11 to 15 °C on the highest grounds. There can be remarkably cool weather in the interior with warmer wet season starting in July and ending in December–January with colder dry season starting in December–January and ending in June.
The major climate risk, similarly to other Cape Verdean islands, yet much less pronounced in the higher altitudes due to better ability in gaining moisture from clouds, is drought.