This national park, one of the largest in Europe, occupies marshland at the mouth of the Guadalquivir river. It has a fragile ecosystem and is an ideal refuge for migratory birds. The park comprises three different areas: the salt marshes (marismas), the sand dunes, which advance inland at a rate of 6m a year, and the cotos, covered in scrub. From its visitors’ centres, it is possible to explore the park on foot, by four-wheel-drive or on horseback (prior booking required for all tours).