I think too they were Anunnakis or related to them who constructed these site. What it comes to Russian- Anunnaki- relation, Scythians descended from Sumerian priestly class and Sumerian priestly class from Anunnakis, I think. Furthermore, there are GIANT mosaics (and totally unknown?), presenting Euripides and aliens, in the Amurskaya region. All the foundations are made in the same way, also a road or a structure leading to the Kondyor Massif. 

amurskaya mosaiikki2

amurskaya mosaiikki5

This mosaic pictured in different angles could present an alien craft In the other hand it could be a giant flower