A good idea for taking maximum advantage from those fantastic summer days it`s to enjoy a unique Dutch experience: wadlopen..... or more simply to get dirty while walking in the swamp trying to reach one of the Frisland islands.
Of course, hope to get to your destination before the high tide catches you!
If you do not have any issues with getting mud on your legs and maybe higher, being wet for a few hours, losing your shoes in the swamp, crossing or swimming in the North sea and of course walking for more than 10 km, this experience is for you.
I did it last year from Holwerd to Ameland, 12 km and I can only recommend it: remarkable experience not only for Dutch people :o)
There are plenty of associations organizing those type of walk, all over the summer.
Below some useful links: