In earlier days there was here in the Netherlands a high risk of flooding, dikes were build for protection, but now and then these dikes were broken by heavy storm or/and high tides. When the water rushes over the dikes the water swirled down and created these small ponts, also known as kolk, they are very deep. It was hard to fill up the kolk, thats why the new dike was put around the kolk. Because flooding happened very often and dikes were used as roads, there are a lot of roads which curl through the landscape.
This is the road where I took the picture: