As far as i know, it used to say "Guten Tag in Beelitz Heilstätten"
A huge hospital complex near Berlin that was built in the late 19th and early 20th century. It has been used as a sanatorium and later as a war hospital by the Germans and the Russians. Now it is one of Germany's most well known abandonments and is invaded by hordes of tourists every weekend. I was one of them.