Rent a bike in Amsterdam (if you don't already have one), take the free ferry to North Amsterdam, and cycle 20 minutes to 't Twiske--a large, quiet park with a big lake in the middle, meandering bike paths, bordering pastures with cows, horses, and goats, free swimming beaches, rest rooms, a lovely windmill, a little restaurant, and a small marina. Great pause from the busy, crowded, hot city.