Here are some beautiful entrance halls in St. Petersburg with free access.
Keep these addresses:
BLUE
Kanshin Mansion
Kuznechny Lane, 6
YELLOW/DAISY
Lomonosova Street, 14
GRAY
Open during working hours
Lev Tolstoy Street, 1-3
NEAR KAZAN CATHEDRAL
Kazan Street, 7
Open during working hours