A jewel of the National Park system, Cape Cod National Seashore hosts two visitor centers on the Cape, in Eastham and Provincetown. Both include wonderful visitor buildings that lay out the ecology of the region, and are staffed with rangers who lead tours and are there to answer questions about the park. Both centers are situated on large swaths of protected lands replete with trails and water access for ranger-led hikes and water tours. Check out their respective websites for activities.