Naturalis is the Dutch national museum of natural history and one of the largest natural-history collections in the world. The 2019 rebuild gave it a striking modern home next to the Leiden Central Station, with daylight galleries and a deliberate focus on biodiversity rather than dusty cabinets.
The dinosaur gallery, featuring Trix the T. rex, is the headline draw, but the live insect room, the deep-sea hall, and the iceberg simulator are all worth your time. It's one of the few museums in the country squarely aimed at children that adults will also enjoy. Allow at least three hours.