the views from the top of st. paul's cathedral are absolutely breath taking, and very worth it! if you can take going up 528 steps varying from very broad steps to narrow tall steps (and taking them all back down to the ground) you'll see london from a different viewpoint. just one note: don't look down!
i also found the entrance to hogwarts at king's cross, of course!! i might be 10years and 2months too late for the start of the year, but i'm off to attend hogwarts school of witchcraft and wizardry~ wish me luck!!