Fernando de Noronha, Brasil. You descend a cliff fissure on iron ladders; turtles below.
Come early or late: between 11am and 4pm in July and August the sand fills up and the car park closes. Off-season the beach is close to empty and access stays open.
The water stays clear most of the year; after days of strong wind it can turn cloudy for 24 to 48 hours. There is no natural shade on the sand, so bring a hat or rent an umbrella at the entrance.