Located in the North of the Island, Singapore Zoo provides an oportunity to see animals from all over the world. The zoo is very nicely maintained and it should be given the steep price of admission. Still it is a very good zoo so if you have time and like seeing animals it is definately a good choice.
Some animals and birds are wandering around (not in cages) the zoo - like this monkey, but not many. The kangaroos are too (they are keep in a large inclosure but they can wander onto the paths people use to walk around).
The zoo lets you feed a variety of animals (for a fee, of course), in addition to tortoises: giraffes and elephants.
Look at how long the arms are on this gibbon!
The Singapore Zoo is expensive but worth it in my opinion (I like seeing animals). The night safari isn't worth it I don't think. I thought it sounded interesting but you really can't see much. And if you spent a good deal of time walking around the zoo all day it is tiring. The best part of the night safari was the dinner. It isn't even really part of it, just something to keep you busy while you wait for the night safari to open, but the food court food was actually pretty good and not outrageously expensive. You can certainly find better food, but I was very pleased with how good it was.