I haven't been to Stonehenge, but I've been to a similar, older site in Ireland called Newgrange. This is the oldest solar observatory - even older than Stonehenge and the pyramids. On the morning of the winter solstice, there is a little gap above the door that aligns perfectly with the Sun, filling the chamber with light. This is very impressive, given that it was built thousands of years ago!

Yes, I've been to Stonehenge too... nowadays you can't get as close as you used to be able to. Another interesting solar alignment in the Americas is Chaco Canyon and many of the Mayan pyramids, like Chichen Itza. That is neat to go at the equinoxes (to see the snake traveling down the edge of the pyramid), or the solstices (alignments of pyramids).