Founded in 1752 as a menagerie by Franz Stephan, Tiergarten Schönbrunn, or Vienna Zoo, is the oldest zoo in the world. It houses some 750 animals of all shapes and sizes; the most recent arrivals to excite crowds were giant pandas in 2003 although lemurs, armadillos and baby Serbian tigers spurred plenty of interest in 2006. Thankfully most of the original cramped cages have been updated and improved, but the odd one still remains.
The zoo's layout is reminiscent of a bicycle wheel, with pathways as spokes and an octagonal pavilion at its center. The pavilion dates from 1759 and was used as the imperial breakfast room; it now houses a fine restaurant (so you can feel regal, too). Feeding times are staggered throughout the day - maps on display tell you who's dining when.
Metro U4 goes there, stop Hietzing. Also trams 10, 58, 60 and 61.