Like in most places related to Peter the Great Marine Fortress are parts of the tunnels in this area home for bats.
Coordinates might not be exact. Just use your eyes, no need to dig.
You can check out one of the recordings of the fortress on this site:
https://mapsengine.google.com/maps/d/viewer?mid=zPslYwoImf-g.kCj2L2q5JtVA&usp=sharing
Nearby Kiia village is among the smaller ones in Saue Parish.