Klangturm, Observation tower in St. Pölten, Austria

Klangturm is a 77-metre tower in the Landhausviertel of St. Pölten, built from 650 tonnes of steel and 1,000 m² of glass on a 15 by 15 metre base. Three walk-in steel spheres, each 5.70 metres across and weighing almost nine tonnes, sit in 8 by 8 metre rooms about 13 metres high and serve as listening zones. A panoramic lift or 280 steps lead to the terrace at roughly 47 metres; the roof carries broadcast and mobile-phone antennas.

Lower Austria's provincial government moved from Vienna to St. Pölten in 1986, requiring new buildings for government and cultural institutions. The Klangturm, designed by Ernst Hoffmann, who planned the entire Landhausviertel, was built in 1996 and opened in 1997. At the opening of the new Landhaus on 15 November 1996, the tower's interior was unfinished, so it 'sounded' only outward with the multimedia concert 'Land im Klang' by Alvin Curran and Uli Sigg. The tower first opened to the public on 13–14 September 1997 with 'Einhören'.

The three sound spheres, each 5.70 m across and nearly nine tonnes, host installations that use their acoustics; the first three levels are re-equipped by different artists every year. Curator Mia Zabelka launched the 1997 opening programme "Einhören" with touchscreens, a theremin and the children's level "Global Kids". The exhibition area is unheated, so it is used seasonally from April to October.

The viewing terrace sits at about 47 metres and is reached by a panoramic lift or 280 steps; the exhibition levels are not heated, so installations run seasonally from April to October, while the info centre and terrace stay open all year. Bus lines 2 and 9 run from St. Pölten's main station directly to the Landhaus Süd stop below the tower.

The three spheres inside are 5.70 metres across and weigh almost nine tonnes each; they serve as walk-in listening zones, not decoration. The tower's steel-and-glass shell also carries broadcast masts, a weather panorama camera and mobile-phone antennas on the roof.