You can't really call the Kula Tower in Belgrade a skyscraper - the building has only 42 floors. Still, the observation deck is high enough for tourists to get great shots from up there.
The observation deck has a great location - you can see all of Belgrade in every direction. To get there, you don't need to go straight into the tower. We first tried doing exactly that, but those entrances only lead to the hotel and apartments. Access to the deck is through the neighboring shopping mall. Go into the mall, head up to the next floor, and walk toward the tower. The mall is connected to Kula Tower by a long pedestrian bridge - you need to cross it.