Dudes, it's Stone HENGE.
That's far away from London.
I have not been there since 2000. I used to go almost every year between 1993 and 2000, when I was a bartender making big bucks. Now I'm a teacher and I make less. 9/11 kind of soured me on international travel too. There is so much to see in London, you're not going to be there long enough to do much of it.
Not all pubs are like BLT said. It just depends on where you go. Not everything is served room temp. You have your choice of beers. The hand pulled ales are served cellar cool, and are not artificially carbonated. Most Americans don't like it. Lagers and stouts are always served cold. Guinness is even sometimes served, "Extra Cold". Try the hard cider. It's awesome. If you get a soft drink, it will come with about 2 ice cubes. Like BLT said, you have to ask for more. Roundabouts are an awesome driving experience. Much better than the idiotic intersections we have here.
As far as what to see, I don't even know where to start. Being a history teacher, I absolutely LOVED the British War museum. Riding the "Tube" is the best way to get around London. In my opinion it is the best subway system in the world. I suggest you get a day ticket on the red double decker on/off tour busses. It's a great way to see most of the city and you can get off and see things up close if you like. You really can't go wrong.
Just so I can toot my own horn for once, I was once announced at the House of Lords in Parliament. I'm a descendant of Prince Henry Sinclair, Knight Templar, and I was there for a Sinclair Clan reunion. It was an awesome experience. We had a hoity toity reception afterwards right on the banks of the Thames. My cousin got so sloshed, he puked in the river. LOL!
If you get out of London at all, you need to see the "Cotswolds". It's a set of hills to the west of London. Find the tiny village of Castle Coombe. It is a trip back in time I tell you. Also Warwick Castle, which is the best in all of Great Britain in my opinion is there.
Do enjoy yourself. St. Paul's Cathedral. Take the walk up to the top. It's worth it. - Sandy