Fascinating stuff David! Does your research suggest that (astronomical) observations were made principally from inside or from outside of the structure (or perhaps equally from both?).
From a different time (7th century) and a different place (South Korea) there are the stone tower observatories – Cheomseongdae perhaps being the most famous. More here –http://www.newworldencyclopedia.org/entry/Cheomseongdae (Cheomseongdae means ‘Nearer the Stars Palace’ :-)