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.
A few years ago, the Volkskrant (one of the countries biggest newspaper) moved office to a new location. Their old headquarter now houses hundreds of artists and musician; along with dance studios, a bar/club with panorama over the city, a dreadlock 'doctor', a Russian cultural centre, a cyberpunk gallery and my photo studio on the 4th floor. It was a conscious choice by the founders to create a total melting pot. In the basement for example, 3 doors away from our music studio, you will find some cheerful weed smoking hiphop producers from the Bijlmer (the 'ghetto' of Amsterdam); an ex-yougoslavian hardcore drummer with a full analogue recording studio and a ballet school run by an obese woman in her 70's. Ok, it might seem artificial, but it really is quite magical!