In London, like most European cities, many of the key landmarks are within walking distance of each other. That said, there is a great deal to be said for getting high up for an over-view of the place.
I remember watching the London Eye being slowly put in place just before the turn of the millenium as part of London's celebrations for the year 2000. This grand ferris wheel (135 metre, 443 ft) was meant to be temporarily situated on the banks of the Thames just across from the Palace of Westminster, but here it remains to this day.
If in London I would recommend, if you have the time, to head to Westminster underground, see the British Parliament, cross Westminster Bridge and hitch a ride on the London Eye. It takes about half an hour for one revolution, and the views are simply great. You can do your sighstseeing in one panoramic visual feast. Go ride - enjoy!
