This is what it looked like when I entered Freiburg through it in September 1992. That picture shows a construction site over to the left, where the new hotel is. Here is another view from 1970.
A few years after I arrived, the city replaced it with the modern building we have today. It is further from the street, includes a mall, and has a tower with photovoltaics on the southern façade. At the top, there is a club where you can dance overlooking the town, and below it you can have brunch on Sunday – including a chocolate fountain. I was once interviewed there by BBC World. I took the picture below from the main solar tower towards the north. You can see the smaller tower on the left, which also has solar on the façade.
And here is the main Solar Tower as seen from the streetcar bridge: