Going with the flow... Rangiroa in French Polynesia is famed for wonderful diving, but snorkellers too can get in on the act at one of the greatest of all marine sites - Tiputa Pass.

1,500 sharks

The tidal pass from open ocean into the Rangiroa lagoon funnels vast numbers of fish and their larger predators through a narrow gap in the reef, and marine biologists have counted as many as 1500 sharks around the mouths of the pass at one time.

This may not sound like the best place for a snorkel, but with visibility of up to 40 metres a regular occurrence, snorkellers can watch the action from a safe distance. Even better this is pretty much effort free, as you plop off the seed of the boat and, taken by the strong current, you join the marine migration drifting along above sharks, manta rays and thousands of colourful reef fish. Wonderful.