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Bonus badly framed shot of a 60s tram next to the newest one (there's a few ones running already but the manufacturer, Alstom, is years behind schedule on production... I think the city's waiting for 30+ trams that were supposed to be in service by now): 
Have fun! Be aware though that they only open once a month (next is Dec 14th) and will go on winter break until March soon. See hsk.koeln for more info.