St. Mary's Islands, Rock formation in Udupi district, Karnataka, India

St. Mary's Islands is a group of four uninhabited islands in the Arabian Sea off Malpe, Udupi district, Karnataka. The northernmost, Coconut Island, about 500 m long and 100 m wide, exposes columnar rhyolitic lava: tightly packed hexagonal and polygonal pillars, the tallest about 6 m, with flat tops, tilted clusters and broken blocks.

The rocks formed around 88 million years ago through volcanic processes, when Madagascar separated from the Indian continent. European explorers reached the islands in the late 15th century during their first voyages along the western Indian coast.

The name comes from Vasco da Gama, who landed here in 1498 on his voyage to India, set up a cross and called the island O Padrão de Santa Maria, the Pillar of St. Mary, in Portuguese. The islands are also called Thonsepar, meaning Coconut Islands, for their coconut trees. No one lives on them.

Ferries leave from Malpe Beach and bring visitors across in a short crossing, with boats running mainly during the cooler months from November to February. Tides affect how much of the rock formations is visible, so it helps to check the water level before going.

The hexagonal columns resemble structures found in only a few other places in the world, including the Giant's Causeway in Northern Ireland. At low tide, visitors can walk between the rocks and observe the geometric shapes up close.