In November 2021, we had a one-night stop in Magdeburg on our way to Hamburg. While there is not much to see there (the city was heavily bombed during WW2 and then became part of DDR so lots of buildings are from communist times), I realised that it has a Hundertwasser building and that you can sleep there, as it has a hotel in it! It was actually quite an interesting building, with multiple sections and inner yards. The hotel part if quite small, actually. The rest is mostly residential and there are cafes, restaurants and small shops spread around.
We did not have time to visit the Cathedral, but it seems to be the oldest Gothic cathedral in Germany, built between 1209 and 1520!
