Frostbrunnsdalen, Nature reserve in Dalarna, Sweden

Frostbrunnsdalen is a ravine about 20 metres deep and roughly 1,100 metres long, cut by Frostbrunnsbäcken through the loose soils of the Tunaslätten plain just west of Stora Tuna kyrka. The nature reserve, established in 1978, covers about 31 hectares. Its slopes are dominated by deciduous trees such as aspen, bird cherry and grey alder, with some spruce and pine.

The area became known in the 1800s for its natural mineral springs and once hosted a spa facility with bathing areas. After that operation ended, the valley returned to nature and was later protected as a reserve.

The name comes from the cold springs that define the valley and have drawn people for centuries. Today the landscape serves as home to rare butterfly species and forest birds that visitors can observe while walking quietly.

Marked pathways make exploration easier and visitors should stay on them especially between mid-April and late June when the terrain is most sensitive. Dogs must be leashed at all times, and camping or parking recreational vehicles is not permitted.

Strong groundwater flows emerge through fine-grained soil and create a network of natural springs throughout the valley. These waters eventually feed the Tunaån river, giving the area its distinct moisture and lush plant growth.