Red Square and the Kremlin
I believe Red Square will always be dominated by St Basil's
Cathedral, completed by Tsar Ivan the Terrible in 1561.  Ivan
constructed this masterpiece, symbol of Russia, to
commemorate military triumphs and/or as a penance for his   
many sins.  Ivan still continued the execution of his enemies in
Red Square, another Russian tradition.
You can see my best full-size picture of St Basil's by clicking
here .  The individual domes also deserve their close ups.         
The first dome above may be more ornate, but this St
Basil's red and green combination is also stunning.
Since his death in 1924, Lenin's body has been
displayed/preserved in this Red Square tomb, next to
the Kremlin's walls.  I visited him in 1989, and Lenin
appeared quite vigorous, wearing a suit and tie.  The
lines were gone in 1996, but Lenin could still be
viewed. Apparently he is not going anywhere.   
The Kremlin itself consists of red walls and towers
on the outside.  The interior includes governmental
buildings (guarded and off-limits), plus many tourist
attractions/museums that are open to the public.  
Tsars did not believe in separation of church and state.  The
Kremlin interior's best photo opportunity is Cathedral
Square, a cluster of several historic Russian Orthodox
churches.  On a dark day, these were my best golden domes,  
If you have a high speed internet connection, watch the Intrepid
Berkeley Explorer's free video of this trip by clicking on:
Tsar Trek