A horror movie from the 60s, egg-like object

My mother asked me to help her identify a movie she would like to rewatch. Her memory of it is sketchy at best though.

The movie was released sometime in the 60s, it was in color and it was probably British production.

She recalls a man going through a forest following some feeling. The man encounters a fence with various warnings, passes that fence and finds something resembling a huge spider egg. That egg is emitting some waves that cause anxiety.

Edit: additional details:

Lengthy sentences of going through the forest, the man is visibly lost, but drawn (by a feeling) in certain direction. It lasts for quite a while - nothing an action-packed series could afford, definitely a style of full movie. No catchy "action" music, mostly just rustling of leaves. Dry underbrush, fallen leaves - early spring or late fall. Later, upon finding the fence, he sneaks along the fence trying to spot whatever's inside for quite a while until he finds a spot with a view to the inside. The orb structure is a huge sphere - there are other buildings around it, and they are small by comparison.

I'm not quite sure if it's 60's - the clothes of the protagonists are "fashionable" 60's clothing - slightly too short, slim trousers, a kind of hip suit.