The Royal Tyrrell Museum is the anchor of a Drumheller day. Its dinosaur halls are large, serious, and still easy to enjoy if you are not a fossil obsessive, with mounted skeletons, ancient plants, marine reptiles, and displays that explain why this valley preserved so much life from the Cretaceous period.
Leave time for the short trails outside the museum. They are a good first look at the badlands themselves, not just the bones that came out of them.