Jamtli is an open-air history museum just outside the centre of Östersund, and one of the best of its kind in Scandinavia — which means one of the best in the world. The outdoor section reconstructs Jämtland farm life from the 18th and 19th centuries using original relocated buildings, with costumed interpreters who work in the buildings, cook on open hearths, tend animals, and interact with visitors without breaking the historical frame. In summer the effect is immersive in a way that photographs can't convey.
The indoor museum building holds a strong collection covering Jämtland's history from the Stone Age through the 20th century, including the Överhogdal tapestries in their own dedicated gallery. There's also a good exhibition on the history and culture of the Sami people of the region. The museum café serves traditional Jämtland food — open sandwiches with cured reindeer, coffee served the Swedish way — and the whole site is large enough to occupy a full half-day comfortably. Buy a combined ticket that includes both the outdoor area and the indoor museum.