The oldest part of the continents are probably what you're looking for. South central Africa, corresponding parts of Brazil, Australia, and parts of eastern Ca

The oldest part of the continents are probably what you're looking for. South central Africa, corresponding parts of Brazil, Australia, and parts of eastern Canada are all very old, multiple billions of years old. But really, these are VERY old areas. Lots of things have happened to them in that much time. Some of them were undoubtedly wet.