Megalithic setting for forest spring

In a forest not far from a hamlet near Calw in the northern Black Forest, there is a small spring that literally poses great puzzles. The ground there is not necessarily particularly tread-resistant (at least not in winter, autumn and spring). Nevertheless, great forces must have been exerted at the time to cover this spring.

The heavy terrain, side walls weighing tons and an equally massive ceiling slab raise the question of who this spring was once so important to. And above all: how did the components get there?
A quick look under the lid showed us that it doesn't go deep here. But that was all that could be determined there.

We stayed there for quite a while, this spring is really interesting. The water escapes from an outlet in the side wall and then follows a stream course. At the side outlet itself, there is practically no flow speed to be felt or observed at all. Only when you follow the stream for a few metres do you notice a slight current that keeps the water moving. Otherwise, one could easily assume that the spring has long since dried up. So despite the fact that the water looks stagnant, there is still plenty of activity here.

Here in the picture: A small stream develops from the trickle. The water flows out of the spring practically imperceptibly from the lateral outlet opening.

Outlet on the underside; engravings in the area of the side walls.

Why is the lid round and not square? It would have been much easier. Does the contrast of the symbolism "square-round" play a role? Or am I reading too much into it?

You don't find a spring like this every day, and the importance of this place was obviously obvious to the ancients. Is it a sacred or magical spring? You don't stumble across places like this every day.