I've never heard of Namsterdam, but I know of several places in Vancouver like that.
Of course, why even bother... just pick some random back alley downtown and chances are there'll already be someone else back there who was thinking the same thing.
I for one use to do it all the time just walking around from place to place. The worst that could happen is you lose your baggy and get your "name written down" i.e. the cops will know whose stuff they yanked when they're smoking it themselves 15 minutes later and laughing about it.
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