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Dominica’s pre-eminent trek, and one of the hardest, travels 4 miles to a 207ft-wide boiling lake, which is actually a flooded fumarole – a crack in the earth that allows hot gases to vent from the molten lava below. Take the trailhead at Ti Tou Gorge and budget no less than six hours for the round-trip.

It's the world’s second-largest such lake (the largest is in New Zealand). Inexperienced hikers should consider hiking with a guide (about US$40 per person, more with car transfer).