Truvorovo Gorodishche is the older Izborsk: a raised settlement site north of the present fortress, with earthworks, a cemetery, and views over the lake. Most of what you see is grass and contours, so it helps to arrive after seeing the fortress; the contrast between early settlement and later military stonework is the point.
The attached legend is stronger than the evidence, but that does not make the place less evocative. The cross, the small church, and the exposed hilltop give Izborsk its older, almost mythic layer.