Balsthal, at the exit of the Klus Gorge which connects Oensingen to the Solothurn Jura, is the gateway to the Thal Nature Park, a very hikable area just a few kilometres from the urbanised areas of the Jura foothills.

Main sights (according to Wikipedia):

The former parish church of Notre-Dame, built on Roman and early Christian substructures and consisting mainly of elements dating from the 16th to 18th centuries.

Herrengasse with the neo-classical former administration building (Altes Amthaus), the early Baroque Zum Kreuz inn from 1621, the Biedermeier Rössli and the former granary.

The Chapel of St. Anthony, which has vaults with Baroque paintings from the early 17th century, and the Chapel of St. Odilia, built in 1511, which has rigid Gothic sections to which important additions were made in 1662.

Finally, the Paper Museum, housed in a mill dating from 1773.

Useful links

Swiss Canton of Solothurn (iSwitzerland Guide) - Wikipedia