Go to Stonehenge in the winter. There will be fewer visitors and if the weather is miserable, cold or even snowy, you will enjoy the atmosphere of the place so much more than on a hot summer's day with half a million tourists and their coaches getting in the way. Last time I visited you couldn't get very close to the stones - understandable given the numbers there - but years ago, before the tourist boom, I was able to walk amongst these monoliths and touch them. They've been there for 4000 years and when you see them you can't help but wonder why and how they got there.
While you're in the area, go to Avebury as well - you can walk amongst the stones there.