I think you're getting overexcited - the "ghost stations" were U-Bahn and S-Bahn stations that were closed during the Berlin Wall era, as they were on lines that were mainly in West Berlin but briefly passed through East Berlin, so the trains would run through them without stopping. All of them were re-opened and renovated fairly soon after the Wall fell. So the tour will be about the history, but you won't be going anywhere that isn't accessible to the general public nowadays.
As Henry said, there is a historical exhibit in part of Nordbahnhof S-Bahn station. As I remember it's just some text panels on the walls, but it's interestingly in-depth and I think it's bilingual English and German.