While somewhat later are the more famous stone circles such as Avebury (near to West Kennet, and part of the same 'ritual landscape')
In general, through human development it has become more and more difficult to contact the divine. And this may be related to the assumed whereabouts of the divine.
Probably (there are no records), the earliest humans lived always 'in' the divine world - there was no separation between divine and mundane. Later, among the recorded simple hunter gatherers - contact with gods and spirits was more difficult; only attainable intermittently by a minority of specialist 'shamans' - who had to undergo some training, or else learn to use altered conscious states.
I would guess that the next stage - after the development of agriculture, and corresponding to the early Neolithic as at West Kennet - involved a professional priesthood, each of whom would experience a prolonged initiation. And also sensory deprivation and isolation - hence the underground sacred places.
(The Pyramids of Ancient Egypt are likely a highly developed version of this - the inside of the pyramid being the sacred space.)
Under-ground was also the place of the divine - corresponding to the intuition that the divine was 'within' everyone and every-thing.
The monument Seahenge had an upside-down oak tree at its centre - roots above the surface, trunk and branches projecting deep into the earth - perhaps linking the divine underworld with this mundane surface world...
In the later neolithic, and into the bronze age - it seems likely that the contact with the divine became even more difficult - such that the gods were no longer experienced 'inside' - but in the sky, far away, imperceptible - and only indirectly and abstractly contactable by such methods as divination.
Hence the great stone circles (and pyramidal 'mounds' such as Silbury) were 'sky temples' - astronomically-shaped and aligned. I also assume that there was a supreme single god, by this time (henotheism); corresponding to centralised priestly government. 'Heaven' also means sky.
(The gods-under-ground, and god-in-the-sky temples seem to have co-existed for a long time - perhaps catering to different types of person; but the distinct impression is that the sky temples to the supreme god had the highest status, at least among the ruling group - since the greatest efforts were put into these structures.)
By this point, the kind of knowledge-based, abstract, priest-led religion was established which survived (gradually changing, becoming more theoretical and less direct) right through to the Reformation, and (somewhat modified) into modernity - after which it declined.
Until, from the advent of modernity (?1500s) increasing up-to nowadays, most people cannot contact the divine at all, under any circumstances - and deny its reality.
The idea of Romantic Christianity is that - starting with a few people from about the middle 1750s, and increasing, modern people are implicitly aware of the divine in a different, and individual, way; but which is not recognised as divine contact.
This is the process of conscious intuition, which I have often tried to describe on this blog. My understanding is that it happens to many (or most) people - but that nearly-always its validity is denied, and it implications ignored.
The modern sacred space is each Man's consciousness.
Note: If you are interested by the above line of argument, although not the specifics, you can find it superbly explored in Jeremy Naydler's The Future of the Ancient World, 2009.
