As it happens, the valley’s architecture includes more buildings from the medieval period than any other district in Norway, said Anders Dalseg, a consultant for the Setesdal Museum who restores the old lofts and teaches courses in restoration. Twenty percent of Norwegian buildings constructed before 1650 are in Setesdal, including 18 built before 1350, he said.

The medieval buildings are only the most visible sign of Setesdal’s deep cultural roots. Perhaps more significant is the valley’s fiddle tradition, which encompasses some of the oldest music in Norway and has long drawn interest from musicologists and musicians from around the world. The weekend celebration we attended included a concert by two of Norway’s master fiddlers, Hallvard T. Bjorgum and Gunnar Stubseid, both of whom live in their native Setesdal villages. For the concert, an upstairs room in the Setesdal Museum, built 25 years ago as a cultural center, was packed with people sitting on the floor and standing at the fringes. Some had driven for hours to hear the men perform.

The fiddlers sat on folding chairs, casually dressed in T-shirts and conversing with the audience between numbers. Their instruments were Hardangerfeles, beautifully decorated fiddles with double sets of strings tuned in unique ways for different songs. The upper strings are fingered and bowed much like any fiddle, while the lower strings vibrate sympathetically and create a continuous, droning melody. The effect, along with thematic repetition and rhythmic intensity, is mesmerizing. (In fact, one subset of Setesdal tunes is called rammeslatt, or strong stroke, and is said to cause trances both in the fiddler and the audience.)

On this Saturday night the melodies varied from rollicking to plaintive, with percussion created by the performer’s stamping feet. Mr. Bjorgum, who was knighted in 2016 by the Norwegian King Harald V for his significance to Norwegian folk music, explained that many of the songs had been saved from extinction by a fiddler named Dreng Ose, who traveled to Minnesota’s Red River valley early in the 20th century to learn tunes that had been carried by emigrants to the United States. It was a critical rescue mission because the music could be learned only by one fiddler from another. (In a modern twist, one young Setesdal fiddler told me that he now learns tunes on Spotify and then visits his teacher for refinement and correction.)