720-ton tuned mass damper in Taipei 101, a Taiwanese skyscraper that is one of the tallest in the world. Many tall buildings have these, especially those in places prone to earthquakes. This one is rare because it is open to the public.
In this 2:15 video, you can see the ball swinging during the 2008 Sichuan earthquake.
Emergency building escape mechanism - GIF and video
Floor-by-floor Japanese building demolition - GIF and video