This is the biggest park in Amsterdam and is all man-made. It was actually a project put together to give people jobs after WWII. There is no lack of activities in this park though.
If you are feeling the need to get away from the cars, bikes and many people of the city, this is a great place to go. With so much space, even on a nice day it never feels crowded. You could spend a couple hourse just lazily riding through the trees or walking around the many foot paths. It is also possible to rent horses here and there is a good amount of horse trails throughout the park.
In the middle of the park, there is a lake where you can rent kayaks, canoes or paddle boats. For about 6 euro an hour, you can paddle around the many canals. Just another great activity this park has to offer.
To end the day, up near the Bos Museum, which is in the northwestern corner of the park, there is a restaurant serving some of the best pancakes in town. Great way to end a day at the park! Open 'til 7pm.