This scene was a bit cluttered when we were there. Big dos going on for graduations.
I believe that this is the Orlov Palace. Catherine II had it built for her lover Grigory Orlov. Twas he and his brothers that plotted the coup and offed Peter II for her, and Grigory remained a loyal soldier and diplomat for her long after the relationship cooled. Unfortunately he died before moving itnto the palace.
Catherine II always made generous settlements on her exes and remained on good terms with them after the breakups.