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If you don't want to leave the building and go to the Visitor's Park you could visit the Visitor's terrace which offers a great view to the apron and currently the construction site of terminal 2's new satellite building. The terrace is located outside the secure area. The entrance is located in the upper floor of the public area of the terminal.
Source: flickr user Curimedia | P H O T O G R A P H Y, CC-BY 2.0.