Featuring more than 10,000 animals, Vienna’s Aqua Terra Zoo occupies one of six massive concrete flak gun towers built by the Nazis shortly before the end of WWII. The huge space is divided between terrariums, aquariums and aviaries. Highlights include the feeding of the sharks and piranhas (Mon at 10:30 & Fri at 15:30) as well as other animals (posted online). Thrillseekers may find a trip up the rock climbing wall on the outside of the flak tower a fun jaunt before viewing the weekly shark dive (Thu at 18:00).