When people, especially those who don't live in the UK, think 'London', an image of the Big Ben usually comes to mind. That huge clock, adjoining the Palace of Westminster, standing tall & chiming loud... What most people don't know is that Big Ben does not refer to the clock. Big Ben is the bell housed within the clock tower. Nowadays, though, people usually refer to the clock tower using the same name.
There isn't actually anything much to do at the Big Ben. Stand nearby and listen to the chimes, maybe. UK residents can explore the tower after obtaining permission, but tourists aren't allowed to. Still, you don't feel like you've seen London until you've at least walked past this great old clock.
...and the new
From Big Ben, walk down Westminster Bridge Road (that's the bridge near the clock tower) to the London Eye. One of the more modern tourist attractions, this is something like a giant Ferris Wheel which offers you a view of pretty much the whole of London.
The London Eye is pretty expensive though, and also kind of boring, considering you don't do anything other than stare down from a slow-moving glass cabin. If Ferris Wheels are your thing, or if you want to see everything in London but don't have the time to actually go exploring, then you might enjoy this. Otherwise, you might want to give this particular attraction a miss.
And now, I gotta run, 'cos the London Tourist Board or whoever's in charge is gonna come after me.
