The North Museum, on the campus of Franklin and Marshall College a short drive north of downtown, is Lancaster's natural history and science museum. The collection covers regional geology, Native American archaeology, taxidermied wildlife of the Susquehanna Valley, and a small but well-restored planetarium.
It's aimed mainly at families, but the geology and Native American galleries are worth a stop for adult visitors as well. The planetarium runs short shows on weekends — check the website for times.