If you troll around long enough in the National Cathedral, I would imagine you could see everything theoretically, but I haven't lived here long enough yet to do that.  Here are a few treasures I discovered on my last visit.

Memorial for Francis Bowes Sayre who was a longtime Dean and iconographer of the Cathedral

Woodwork on the pews in the Great Choir - the lion and the lamb
Stone from the Appian Way

A wolf in sheep's clothing in the Great Choir

Stone from Mount Sinai, where Moses is said to have received the 10 Commandments
 
All the pews have handmade needle work for the cushions
I liked this bas-relief because after Mary had the baby in Bethlehem, they had to leave the stable and get home for Joseph to work Monday morning, right?