Sited in an 18th century building (added on to over the decades), and reputed to be the oldest museum in The Netherlands, Teylers Museum is an eclectic, fascinating, and important experience.
My visit was on a Saturday. There were plenty of kids there with parents and grandparents, and they were in ecstasy! Bones (, bones, bones), crystals, fossilized fish and skeletons, scientific instruments, rocks, some paintings -- this was the ultimate "museum" of the late 1700's. Reminded me of a cross between Harvard's Peabody Museum & The Castle at Smithsonian in Washington DC. Merchant/banker Pieter Teyler was the founder/benefactor and his curiosity and urge to travel/explore led him to both collect and to categorize and organize these artifacts. He was doing all this at end of 1700's/start of 19th century.
Make sure you allow plenty of time to explore the 2-storey, balconied Oval Room (wherein lie many jewels, rocks, crystals, and scientific instruments). The room itself is a treasure. The entry room is also a gem: nearly circular, with fascinating rounded double doors on all the exits to the various hallways and lovely stonework in the floors.
The Museum has a small cafe with a pleasant view onto a sweet little courtyard outside the 20th Century addition.