The Arizona-Sonora Desert Museum

The ASDM is an amazing place to visit. Much of what is great is covered in the other two comments, but if you are visiting during the summer, I would recommend you go in th evening. During the summer months, the museum is open late. Not only is it much cooler to go in the evening hours, but more of the animals are awake and there are many docents showing off insects and scorpions, bats, etc. I would definitely recommend it!

The Desert Museum is more of a zoo, with many live animals native to the Arizona-Sonora desert.

Make sure you bring plenty of water and come early in the day if you come during the summer (which I don't recommend!). Spring and fall are the best times of year to come to Tucson, and will provide the best chance to see the animals moving around at the Desert Museum.

On the outskirts of Tucson lies The Arizona-Sonora Desert Museum.  No one should ever go to Tucson without a visit to this wonderful place!!

While the name of the place gives the impression of a "museum", that's the furthest thing from the truth.  This beautiful area is actually a world renowned zoo, and a fantastic botanical garden, all in one.  Approximately 85% of the attractions you'll see are outdoors; only 15% will be inside. 

The place is laid out and landscaped beautifully.  You will walk around stunning paths surrounded by all the different plants and flowers that are found in the Sonora Dessert, and it's incredibly beautiful; it also smells incredible. 

There are also a ton of animals here; mountain lions, black bears, gila monsters, Mexican wolves, a ton of different kinds of birds, and more. 

This is a wonderful place to spend a day; especially if you go when it's not too hot.  During the summer, I have to admit that it does detract from your enjoyment when you're roasting the way you will; but the fall and spring are the best. 

Prices are really reasonable; depending on the time of year, it will range between $9 to $12 for adults, and children will be $2 to $4. 

I'm not a big fan of normal zoos, but I really like this place a lot; it's a far more natural surrounding and with such lush vegetation it's just a beautiful place to spend a day!