We climbed the steps to the Whispering Gallery at the top of the dome and it was so cool that we spent a good half hour up there. How it works is you whisper into the wall and people on the other side of the dome can hear you perfectly! It was a fun game for sure. I had to sneak this picture in before I was reprimanded- the guards could have just whispered into the wall and gotten mad at me without ever having to get up so I had to be quick.
Here's something I learned today: Sir Christopher Wren was not only an architect but an astronomer as well and designed St Paul's to be exactly 365 feet tall because that is how many days it takes the Earth to orbit the Sun. There's your fun fact for the day.