Well, I don’t know about visiting all the world’s tallest buildings. but i did visit the world’s tallest building as of 2010, the Burj Kalifa located in Dubai.
World's Tallest Building, The Burj Kalifa in Dubai
They only let you up to the 124th out of 160 floors of the tower
Burj Kalifa Observation Deck, 124 stories up
Even only at 124 stories up look how tiny it makes the other “sky scrapers” look.
Burj Kalifa overshadowing the other "sky scrapers"