When Christopher Wren completed St. Paul's Cathederal, Queen Victoria felt it was somewhat stark.  After viewing Westminster, in all it's grandeur, I can understand why she may have felt that way.  It was Queen Victoria that commissioned the amazing Byzantine style mosaics that make up the ceilings in much of the Cathedral today.  The light catches the surfaces of the tile pieces differently with each step you take, and gives them an appearance of sparkling.