Clearly great minds think alike. As I was downloading the pictures I took on Monday's Mayday stroll through Prenzlauer Berg, a journalist at Welt am Sonntag was writing the story of the building whose picture I'd taken and about which I wrote yesterday. It was the party headquarters, as I'd thought, and later became the Institute for Marxist-Leninism.
But what I didn't realize, and the article mentions, is that it was built in 1928-9 by a Jewish businessman, Hermann Golluber, to house a department store where one could buy on credit -- surely, in those days of rampaging German inflation, a welcome thing. The Nazis made trouble for him, and he and his wife emigrated to America.
And this is why it's still empty. After use as a central headquarters for Nazi youth organizations, it was taken over by the East Germans after the war, but according to the post-unification laws, it's the property of Golluber's heirs, some of whom are in America, others of whom are in Israel. They want a cool €7 million for it, in case you want to open a nightclub or bowling alley of your own and aren't scared by the ghosts which must walk the corridors. And I haven't been inside, but my guess would be that it's a fixer-upper.
(Thanks to Karen for the info!)