Heya! Took this to the concept artist who did the initial treatments on Prif, and he said this (no Reddit account):

It looks cool, just like it. Its a happy coincidence as I didn't have that reference, neither have I been to Russia. I have however been to Istanbul, and Prif was more based on buildings like Hagia Sofia but stretched up to be more gothic, mixed with the ruins of Tintern Abbey - the crystal walls were written about in text before I painted anything. If you look up those two places it makes sense combined.