Actually, Stonehenge was fairly interesting.
To answer the MAQ: no, it's not fenced off. Well, it is fenced
off from the roadway, so that you have to pay a few pounds
to park and enter. And once inside, you get an audio tour
handset. And there is a walkway delimited by some
low ropes, to discourage you from running up and
licking the stones. But I suppose if you felt you really
needed to do so, you probably could, before one of the
guides hurried in behind you to (politely, no doubt
about it) request you desist.