These structures seem to have been made like this (the stone part, anyway). They contain a shape like a gravestone, and a prone circular piece. The standing bit has carvings to identify a ruler.

Bruce records it while Eric and Barbra watch.

Cecily walking with the Trekkers.

This shows a tree shooting up from a ruin.

The guide said it is difficult to keep the parts they have uncovered, let alone clear others.

And ageneral view.