The Black River Gorges are the green heart of Mauritius, a national park of upland forest, rivers and waterfalls that covers a large block of the south-west. The viewpoint on the road along the edge of the plateau gives you the best sense of it, because from here the land drops away in a long wooded slope all the way to the Indian Ocean, and on a clear morning you can pick out the sea on the horizon and the pale line of surf around the reef. When clouds sit low on the plateau, which they often do, the view disappears, and the ride turns into a wet, atmospheric tunnel of trees and mist.
This is a good place to think about how fragile the island is. When the Dutch and then the French settled Mauritius, they cleared enormous areas for cane and brought in deer, pigs and macaque monkeys, and the native forest shrank to a few remnants. A good deal of what remains is here. Conservationists have spent decades pulling a few endemic birds back from the brink, the Mauritius kestrel, the pink pigeon and the echo parakeet among them, and the gorges are one of the places you have the chance of seeing them. You are more likely to see monkeys by the road, and it is sensible not to feed them.
The road across the plateau is a quiet, winding one, climbing through tea and forest and bordered by tall, damp tree ferns. The surface is generally fine but the weather can turn it greasy, and in places there are potholes that arrive without warning. Traffic is thin on weekdays and heavier on Sundays, when families head for the lakes and picnics. The temperature can be ten degrees cooler than the coast, so bring a jacket you will be glad of.
Fuel and food are in the lowland towns, Chemin Grenier being the closest large one, so top up before you start across. There are small stalls and a few modest restaurants near the viewpoints, but do not count on them being open. Carry water, wear rain gear, and give yourself time to walk to one of the lookouts, because the sound of the forest is a part of the place.