Church of the Saviour on Spilled Blood - amazing walls... absolutely icon/mosaic-covered; into every nook, cranny and dome another picture is crammed.
Phenomenal history - somewhat like the Cathedral of Christ the Saviour rebuilt in Moscow in the 1990s (Stalin had got rid of it cos it spoiled his view!) - it had an interesting 20th century... Looted after the Revolution in 1917, closed in the 30s, used as a refuge when Leningrad was under siege by the Nazis in1943-4, then used as a vegetable store!
After 27 years of refurbishment, it was open to the public again in 1997. It never was a consecrated public-worship church, and thus it is now as it ever was, a monument to the assassinated Tsar Alexander II, and a Museum of wonderful Mosaics.