The Unterberg is a prominent summit, 1,342 m above sea level (AA) high, in the Gutenstein Alps in southern Lower Austria.

It is located about 10 km south of Hainfeld and is the westernmost and highest summit of a loose chain of mountains that include the Hocheck (1,037 m) and the Kieneck (1,106 m).

Its crest continues towards the southwest, albeit less high, to the Brunntaler Höhe (1,090 m) and the Leitermauern (1,025 m).

The mountain is made of limestone rock and has a steep, wooded face to the northwest which is pierced by crags, whilst to the southeast it falls away only half as sharply.

The ski lift runs up the southeastern flank to the top and may be reached from Pernitz in the Piesting valley via Muggendorf.