The Ecomuseo de la Fauna is a small ecological museum focused on the birds and wildlife of the Pyrenees, including the conservation work around the bearded vulture. Its setting in Ainsa's castle area gives it extra appeal, since the walls around the museum have fine views over the town and mountains.
It is most useful as a quick orientation stop before heading into the surrounding valleys and national-park landscapes. Combine it with the castle, Plaza Mayor, and the old town.