Here's a close-up so you can see how large, how white, and how beautiful each flower really is:
Another lovely white thing is the dwarf mock orange (Philadelphus), a little shrub only a few feet high. It seems to have suffered some winter die-back this year, and there weren't very many flowers. But the blooms are quite double and extremely fragrant. It's one of my favorite shrubs.
While we're on the subject of white flowers, here's the penstemon called 'Husker's Red' -- but not because the flowers are red. The young stems have a reddish cast and the leaf edges as well, but the flowers are white.