The coastal plain consists mainly of sand dunes and polders. Further inland lies a smooth, slowly rising landscape irrigated by numerous waterways, with fertile valleys and the northeastern sandy plain of the Campine (''Kempen''). The thickly forested hills and plateaus of the Ardennes are more rugged and rocky with caves and small gorges. Extending westward into France, this area is eastwardly connected to the Eifel in Germany by the High Fens plateau, on which the Signal de Botrange forms the country's highest point at .