Lost & Found is a monthly artist salon held in one of the medieval towers of the Waag on the Nieuwmarkt. In the room where Rembrandt's 'The Anatomy Lesson of Dr. Nicolaes Tulp' once took place have since 1997 over 80 sessions of stray images and sound been organized. Artists show material which doesn't fit comfortably into regular gallery contexts; work which demands more concentration than the usual walk-by. Check the Lost & Found website for dates & times.
To get out of the hustle of the city, my husband and I love to bike down to Amsterdam's Forest to see the goat farm, or picnic in the sun. There are also little spots to swim :)
The city's biggest flea market is hosted the first weekend of each month in and around a gigantic warehouse in the industrial area of NDSM in Amsterdam Noord. I love to snuff around the hundreds of stalls to find unusual props. Taking the boat to cross the IJ and leaving the old centre behind is very refreshing. Make sure to also have a drink in Noorderlicht while the sun sets.