Caverns of Time…
Tuesday is for Old Hillsbrad. Head back to the old world (aka. Azeroth), and down to Gadgetzan in Tanaris. Once there, head southeast to the Caverns of Time and take the guided tour. Now you’re ready for Old Hillsbrad.
But why?!
Excellent question. You see, the Bronze Dragonflight is picky about who they want fiddling with the timelines, so you have to finish their questchain in Old Hillsbrad in order to get into Black Morass… and, as we all know, Black Morass is one of the final steps to getting the Master’s Key to Karazhan.