The Westergasfabriek used to be the site of a coal processing plant until well into the 1960s after which it was sanitized, revamped and turned into a park that boasts a number of creative enterprises, clubs and bars in the former factory buildings. Of these buildings the most impressive and distinctive is the Gashouder (Gasholder). Open frequently (but not permanently) for large scale events, concerts and exhibitions, this giant, circular, pillarless chamber with its wrought-iron roof construction will blow your mind.

Source:
http://alicelazarus.wordpress.com/2013/12/09/amsterdam-winter-visit-guide/