No it's not, not unless you have a special reason. If you're a realistic animator working on a sequel to "The Lion King" then by all means go and enjoy yourself, but if you're a cartoonist you might find yourself wondering if the trip was really necessary. Artist-friendly zoos are a myth. Zoos used to be a great places to draw. Older zoos like the one above kept exciting animals like lions in horizontal cages where the lions used to pace up and down for half the day (the other half was spent outside). It was hard on the lion but great for artists who got to see repeated side views of dynamic walks only a few feet infront of their sketchbooks. The cages were indoors and the lighting was perfect for drawing. Best of all, there was no wind to blow your paper and you got to hear the lions roar at each other with the sound echoing off the walls.
Modern zoos put the lions into enormous outdoor habitats. It always takes visitors a minute or two to locate the lion who's usually sleeping behind a rock. No roars, no pacing, just...sleep. If you try to draw the parts of the lion that are visible then you encounter the other problem, namely the difficulty of drawing on reflective, snow-white paper under a blazing sun. Contemporary zoos are not really artist-friendly.
Another myth that artists have is that it's fun to draw at baseball games. Is it? From the grandstands the players are tiny figures that seem to be miles away. If you can see to draw those guys then you've got better sight than I have. It might be fun to draw the fans if they'd only turn around but they won't, unless it's to give you a dirty look for drawing them.
