Maybe only the surface structures. Bilrach has had a good millenia or so of digging down there and plenty of oddly willing slave labor. It looks like quite an engineering feat, but he has plenty of time to build and change it to suit his desires.

The Seren symbology is troubling. It doesn't fit unless the Necrosyrte and Seren were allied and even then, Bilrach and his workers would have removed references to Seren. Given the present fight over the elves, I doubt Seren and Zamorak see eye to eye.