…if ever, visitors from the West were only allowed to visit East Berlin and/or Leipzig (because of the Leipzig fair).That's not true, actually. I have been to several East German cities including Erfurt during a GDR tour back in highschool, also in the 1980s.
How did you manage that? The restrictions were quite heavy for those who wanted to visit places other than the mentioned. Only special occassions such as a 500 year festivity for Luther or so could bring some tourists to the rest of the GDR.