Visiting the Ruhrgebiet

[lordstorm]

I am planning to visit the Ruhr region (Ruhrgebiet) for two days in mid-April this year. I've not been to this corner of Germany before - closest otherwise would be Hamburg or Cologne/Köln - and wouldn't mind a bit of advice in which part of the Ruhr to base myself (if it helps, I'm using rail, taking the train in from Potsdam, and then to Brussels via Cologne by Thalys). As the Ruhrgebiet comprises of many cities, I was wondering which is the best part for me to base myself from for those two days? Bochum? Dortmund? Duisburg? Essen? Hamm? Gelsenkirchen? I'm not really sure what's on offer there culturally or architecturally (two of my biggest attractions to new places) even after reading their blurbs on Wikitravel, so can anyone enlighten me? :)

Cheers,
LS