The Basel Zoo is a must-see if you have a little time left. I always enjoyed being there. For the Bebbies (the people from Basel) it is only called the "Zolli". Opened in 1874, it hosts over 6,000 animals from about 600 species. It is (after the Rhine Falls) the second-most visited touristic place in Switzerland.
In the last years, they made some very special additions. One is the Etosha house, where they simulate African flora and fauna. I am sure the lions will soon not be so shy anymore and let themselves be seen...
In winter, there is the "Penguin Parade". When it's cold enough outside, they take a walk with the penguins. My, they are cute (see pic)!