St. Paul's Cathedral, London

What a delight!  Having been to many churches, cathedrals, chapels, etc in Europe for somewhere to really stick out for me it has to be extra special.  First, the free audio/video guide is top-notch.  The touch-screen multi-media guide is easy, fun, informative and has maps you can 'pinch' to enlarge - wow factor of +10.
There were a couple of architecture students sketching (quite well) the interior.  That's the first time I've seen that inside a building and the reason is obvious, even to a layperson (of architecture) like me.  St. Paul's design is breathtakingly perfect.  The awesome mosaics on the ceilings above the quire were added later and the combination with the unadorned main aisle is a perfect balance.  It was great learning about all the ceremonial things held here like coronations and royal weddings.  My favorite fun fact is that during the women's suffragette movement, a fire was lit under the bishop's chair.  I thought that went well with the Occupy London protesters camped outside St. Paul's.  The down side to that was no tours on the upper floors.  Our tickets are good for a year, so hopefully we'll get back to visit the rest of St. Paul's.  You can take a virtual tour here.

But  the Number ONE thing I loved about St. Paul's was the American Monument Chapel.  From the website:

At the east end of the Cathedral behind the High Altar is the American Memorial Chapel. The Chapel is also known as the Jesus Chapel, as the space was known prior to World War II.

This part of the building was destroyed during the Blitz and as part of the post-war restoration it was decided that the people of Britain should commemorate the 28,000 Americans who were killed on their way to, or stationed in, the UK during the Second World War. Their names are recorded in the 500-page roll of honour encased behind the high altar. This was presented by General Eisenhower in 1951 and a page of the book is turned every day.