I have had only one weird experience at an ancient site. It was at the Hengwm Cairn Circle ( http://www.themodernantiquarian.com/site/2415 ). I was slowly strolling around the circle (as you do) when I felt an irresistible impulse to turn and walk into circle though a gap which may have been a possible entrance. Although I was feeling fairly exhilarated anyway having just had my bacon sandwich and being at a top site, I felt a definite lift on entering the circle. The impulse seemed external rather than internal.