A small community run park just out of town. Good to visit if you haven't seen the ring tailed lemurs yet. They are used to humans here and some of them are tame. You can feed them bananas if you want. A guide tells you more about teh area in a small tour.
One downside is that it ios pretty expensive though.
When you are staying in Ambalavao you should check out the paper factory near hotel aux baugainvillee. You can visit in just an hour or so and it is worth it. You can see how they produce paper by hand from tree bark. They also put in dried flowers by hand and sell it in a small shop. It makes a good souvenir...
From Ambalavao you can rent a car with driver that will take you to the national park office. Here you can buy an entrance ticket and arrange a guide to accompany you in the park. There is also a quite nice photo exposition and other informative displays on ecology and wildlife.
Andringitra itself is absolutely amazing. It is so not what you expect in Madagascar. You are in the mountains here so it can actually get pretty cold. There are great hiking trails with amazing views of stunning rockformations, huge sacred waterfalls, ancient tombs, weird wildlife, caves and rainforests.