The Setesdalsheiene mountain range runs through the municipality, including the tallest mountain in that range, Sæbyggjenuten at . The Byklestigen pass is a torturous trail up a steep cliff face. Until the 1870s, it was the only route to reach Bykle from the middle Setesdal valley to the south. It runs above the river Otra and was the site of numerous accidents on the hazardous route. The eastern side of the valley (and the municipal/county border) is lined by the mountains Gråsteinsnosi, Brandsnutene, Svolhusgreini, Sæbyggjenuten, and Støylsdalsnutene. The western side of the valley (and the municipal/county border) is lined by the mountains Storhellernuten, Skyvassnuten, Sveigen, and Kaldafjellet. The southern border of the municipality is marked by the mountain Steinheii. The mountains Urevassnutene, Djuptjønnuten, Snjoheinuten, and Kvervetjønnuten mark the highlands in the southwestern part of the municipality, northwest of the village of Bykle.