Stonehenge, where the demons dwell, Where the banshees live and they do live well Stonehenge, where a man's a man and the children dance to the pipes of Pan.
Stonehenge started off 5,000 years ago as a big round cemetery for burying grandma in. Then new management took over and decided the place needed a facelift, something to help it stand out in the increasingly competitive prehistoric monument market.
Egypt's innovative pyramid design was creating a LOT of buzz, but Stonehenge looked west instead and negotiated a sweet deal on a load of Welsh stone, carriage thrown in free. It looks as though the instructions weren't included though as the stones got rearranged a few times until they looked right. Meanwhile ancient British engineers had been working on their greatest triumph: two big stones with a big stone on top.
This breakthrough kept Stonehenge at the top of its game until about four thousand years ago when Germany invented the totally sweet gold hat and then the Romans showed up and kept everyone busy building bathhouses and writing poems about their dongs.
The short answer is that it did a lot of stuff. The long answer is that it was one element of an ancient cosmology made physically manifest, embracing the broad concepts of death and rebirth, identity and belonging over a period that saw such massive social and cultural change that to reduce it to a single function is to ignore its diachronic multivocality. Also, there were priests who totally stabbed people.
Because archaeologists can't actually nail down what it was for, the task of interpreting Stonehenge in a comprehensible way has instead fallen to that traditional motor of scientific progress: the slightly deranged amateur. All the most interesting theories about Stonehenge come from retired telephone engineers, hippy astrologers, and heavy metal musicians.
This often annoys archaeologists who thought they had a monopoly on cooking up completely unprovable theories about long forgotten inanimate objects. That's entirely their own fault though for inventing terms like 'ritual significance' and 'funerary landscape' instead of 'sacrificial blood ceremony' or 'dinosaur stargate'.
You can visit Stonhenge today, or if you prefer simply drive past it on the busy trunk road which the British government thinks is an ace way to present one of the world's iconic monuments. After paying English Heritage, the body that manages the site ('manages' in the sense that they've made sure nobody's stolen it yet) to get in, you can walk slowly aroud Stonehenge before sloping off back to the car park via the gift shop. One day there might be a visitor centre but in the meantime it's not surprising that more visitors leave the place believing it to be a landing site for space unicorns rather than well...whatever the hell it is.
You could ask the Neo-druids who like to hang out there what they think, but they are a confused bunch of people whose grasp of theology makes the average Wiccan teenager look like Martin Luther. There's more fun on the summer solstice when you can party with the dreadlocked pagan masses. Bring your didgeridoo and some de-lousing treatment.