M. B. Landstad's 'Norske Folkeviser' (Norwegian Folk Ballads) collects medieval folkeviser from Telemark and Setesdal oral singers, preserving supernatural ballads (naturmytiske) about huldrefolk (hidden mountain folk), nøkken (water spirit), and draug (sea ghost). These lyrical ballads, in 4-line stanzas with omkved (refrain), encode pre-Christian nature beliefs, elf maidens, and transformative shape-shifting folklore from the Norse magic tradition (seid).

Landstad's collection influenced Norwegian Romantic poets (Aasmund Vinje, Ivar Aasen) who wrote Landsmål (Nynorsk) poetry directly adapting ballad refrains, hulder folklore, and mountain spirit motifs against Danish literary dominance. Edvard Grieg's musical settings spread these ballads internationally. The collection's 'supernatural ballad' subtype—where human singers encounter folkloric beings—provided models for Henrik Ibsen's early poems and modern Nordic poets (Rolf Jacobsen). It demonstrates how nature-spirit folklore generates distinct lyric modes for environmental poetics.