The Martinsturm is the most distinctive landmark of the Oberstadt, a medieval defensive tower capped with a huge copper onion dome that gleams green above the old town rooftops. The combination of squat fortress below and baroque flourish above is distinctly odd and immediately recognisable.
The tower dates from the 13th century and was part of the city walls. The dome was added in 1601 at the instruction of the Habsburgs, transforming a purely military structure into something that announced civic pride. Inside there is a small local history museum and a chapel with original frescoes. A narrow staircase leads to the viewing platform near the top, from which you look out over the old town roofscape to the lake below.
The tower is open during summer months. Entry is inexpensive and the climb is worth it for the view if the Pfänder cable car crowds are putting you off the longer ascent.