Who is Anya, Olga from The Madonnas of Leningrad: A Novel and what is their importance?

The elderly Anya and the middle-aged Olga appear in the narrative of Marina's past. Both are employees of the Hermitage who, along with Marina, Viktor, Nadezhda and hundreds of others, take refuge from the Siege's bombing raids in the museum's basement. Anya is a docent, a room attendant who watches visitors to make sure none of the works are harmed. Olga is, like Marina, a tour guide. Anya teaches Marina about "memory palaces" and helps her construct her own memory palace of the Hermitage. Olga is Marina's sometime partner in the regular nighttime, rooftop watch for bombers. Both women survive the Siege, along with Marina.