The Rhoonse Grienden, just like the Carnisse Grienden and the Ridderkerkse Grienden, are so called freshwater tidal fields on the Oude Maas. These old fields lie outside the dike and are under the influence of the ebb and flow of the tide. Large parts of the area are flooded twice a day. As a result, the area has a special flora and fauna. Rhoon Castle in Rhoon is a fortified keep built in 1432 by the Van Duyvelantn family. The castle is located near the medieval village centre, including the village church and the house in Pendrecht.