To be quite honest and very subjective I think they came by sea, of course there may be a third option, Geoffrey of Monmouth has them flying over from Ireland by witch transport, and who am I to argue with some long dead writer of the 12th century.
So to the photos of that strange outcrop in the Preseli Mountains, source of so much dispute and speculation - O for H.G.Well's time travel machine............
The bluestone moved in 1980 I think by helicopter
One of the three great bronze age stone cairns in the centre of Foel Drygarn
Wherever the argument may lead to these bluestones, whether Wainwright and Darvill are right and that Stonehenge was a healing centre, or that the stones were used in a purely decorative form remains to be seen. But there is a very strange air to this bare mystical place in the Preseli mountains and my money is on the bluestones being transported.