Museum de Oude Aarde ("the old earth") occupies a traditional Giethoorn farmhouse on the Binnenpad and contains a private collection of minerals, gemstones, fossils, and geological curiosities assembled over several decades. The collection is broad and genuinely varied — fluorescent minerals lit under UV, large crystal formations, meteorite fragments, and fossils from various periods — and presented in the kind of idiosyncratic, personal way that distinguishes a collector's museum from a corporate one.
It is a good option if the outdoor attractions are hampered by rain, or as a counterweight to the village's canal-and-thatched-roof focus: the subject matter is entirely different and the building itself is worth a look. The museum shop sells specimens, fossils, and geological gifts, including items at prices reasonable enough that children tend to find something they want to take home. Open April to October; check the website for current hours.