Natal is the capital city of the state of Rio Grande do Norte, on Brazil's northeastern tip. It's known for its extensive coastal sand dunes and star-shaped Forte dos Reis Magos, a 16th-century Portuguese fortress at the mouth of the Potengi River. North across the river, Genipabu is an area of towering dunes with a freshwater lagoon. The Via Costeira highway links a 15km stretch of beaches south of the fort.