This is a video one of the kids took. They understood their tour guide to say that there pretty much aren't any houses in the city. Everyone lives in a suite.
Communal flats appeared in Russia in the years following the 1917 Revolution, when the authorities hurriedly shifted the urban proletariat into the flats of the former middle classes and aristocracy. But these places weren't designed for multiple families, so they had to make common rooms. That may mean that a kitchen and bathroom might be shard by eight apartments, for example. The city still has more than 100,000 communal flats, most of them in the historic centre of the city.