NEMO Science Museum is the big copper-green ship-shaped building above the IJ tunnel, a short walk east of Amsterdam Centraal. Inside, hands-on exhibits explain technology, engineering, biology, behaviour, and everyday scientific phenomena in a way that works best for children and younger teens.
The roof terrace is a bonus even if you skip the exhibits. In summer it becomes a free public viewpoint with deckchairs and wide views over the Oosterdok, the old harbourfront, and the centre of Amsterdam.