Castelhanos is Ilhabela's most celebrated east-coast beach and the hardest to reach without effort. The access road crosses the island's spine through dense Atlantic Forest — a 15-kilometre dirt track passable only in 4WD vehicles or on foot — and that barrier keeps the crowds manageable even in high season. The beach itself is about 1.7 kilometres long, set against a wall of forested hills, and has a distinctive heart shape that becomes clear from the Mirante do Coração viewpoint above. The sea faces open ocean, so the surf can be substantial; experienced surfers seek it out, and there are calmer corners near the rocks at either end.
A small traditional caiçara community lives here year-round. Several families run simple restaurants serving fresh fish, lobster, and grilled chicken, and a few offer basic accommodation. At the northern end of the beach, the Trilha do Gato begins and leads through the park to Cachoeira do Gato, one of the island's finest waterfalls. If you don't have a 4WD, tour agencies in town offer jeep excursions to Castelhanos, and boat trips from the mainland channel can also drop you here; the boat option gives you the added pleasure of approaching the beach from the sea.