Het Kralingse Bos
Large park surrounding a lake - quite nice place to relax. Nice place to stop by (there is a parking nearby) and take a walk around. It's a bit strange since it is almost in a center of Rotterdam but when you are there you don't hear the sound of busy city and you can relax and enjoy the nature. It the summer (well... Dutch summer isn't too warm) you can swim and take a sunbath. On the north of lake you have a pier and from it you have a great view of Rotterdam skyline. There are two typical Dutch windmills near lake.