Any 4/20 activities in Amsterdam?

I've been cooped up in London a bit too long (apart from the states I haven't wandered outside in practically a year) so I've decided to head over to Amsterdam for the holiday season...I'm just going for a few days (19th-23rd) but I was wondering if there are any specific goings on in the city for 4/20...?

It'll be my second time going...the first I spent most of it in the red light district too stoned to explore but I do have a list of places I want to go this time (many have been mentioned on here...grey area, de rokerij, siberie, dutch flowers, dampkring, etc...oh and van gogh museum heh). But yeah, I didn't know if any specific places were doing anything special on the day...because I'm sure everywhere will be packed.

Also the last time I went someone mentioned a vaporizer coffeeshop we just had to go to (naturally forgot where though)...anyone know of any and could you explain what one does there (I just smoke joints...never tried a vaporizer).