The trail to Cachoeira do Gato begins at the left (northern) end of Praia de Castelhanos, at the spot locals call Canto do Ribeirão. The path through the park is well-maintained with handrails, a suspension bridge, and benches — a 3.6-kilometre round trip that takes most people about an hour and a half. The forest along the way is old-growth Atlantic Forest, and the contrast between the shadowed trail and the sudden blast of spray when the waterfall comes into view is one of Ilhabela's great small pleasures.
Note that swimming in the pool at the base is currently prohibited: the community of Castelhanos draws its drinking water from this pool, and authorities have been working on relocating the water intake. Check with the park office for the latest rules before you go. The trail is open daily from 8 a.m. to 3 p.m. and is self-guided; park monitors are available to lead groups if you prefer company.