The Manyara Lake National Park is unusual in that it's woody. The lions here have adapated to the environment and it's one of the few places in the world where you'll see them lazing in the trees. The lake, which varies in size according to the season or year, attacts a host of animals that you can easily watch. The park is home to a one of the world's largest populations of monkeys. But beware of the sometimes large gangs of baboons, which can be ferocious!
After visiting, if you've not had your fill, I suggest you head along the Rift Valley on the Karatu road, where you'll find some superb views of the lake.
Even if most tourists just pass through in their four-wheel drives, I really enjoyed my stop at Mto Wa Mbu, which is about 1km from the entrance to the park. It's a pleasant town and its residents happy to welcome a muzungu (white person in swahili) and have a chat.