The beaches on Ons are among the finest in Galicia — white sand, clear Atlantic water, and (because the island is a national park with capped visitor numbers) never the wall-to-wall towels you find elsewhere on the coast in August. Most face east into the sheltered ría, which means calmer water and more sunshine than you'd expect for an Atlantic island.
Melide, in the north, is the showpiece: a wide arc of pale sand backed by low dunes with no development in sight. Area dos Cans, near the ferry pier, is more accessible and fills up first. Between them, smaller coves reward anyone who walks a bit further along the coast path. The western cliffs are not for swimming — that side of the island belongs to the ocean.