Since the summer of 1993, a very special timekeeping device has adorned the banks of the Danube in the Esperantoplatz area. This unique sundial was designed and built by Werner Riegler, a scientist from Grein. It is a so-called equatorial sundial, in which the shadow of a taut wire rope running parallel to the earth's axis falls on a scale. With the help of a semi-cylindrical dial, the time can be read with an accuracy of around two minutes.

The construction of this clock consists of chrome-nickel steel for the frame and brass for the dial and scale. In addition to the time display, a granite globe is attached to the front of the clock. This globe shows the engraved continents and is illuminated by the sun in the same way as the earth itself. The shadow lines on the globe make it possible to recognise in which countries the sun is shining. The special thing about a sundial like this is that it is easy to understand how it works and makes it easy to understand the relationships between the movements of the earth and the sun.