score:7
OK, this turned out to be a quite extreme case of misremembering. The building was in fact Waldviertel Pyramid.
What I got right:
What I got wrong:
The explanation for the last one is also how I found it - I have searched through all .pdf files on ancient sites on my old computer and found it is a pseudoarcheological book, in which it IS claimed to be "of ancient origin".
Last, but not the least. Thanks to everybody.