They stand huddled on the edge of the city, like shabby fortifications put up by an army which has found itself unaccountably short of cash.
Windows stare out with unvarying regularity from row after row of monolithic facades.
It's a far cry from the stereotype of Golden Prague - from here, the Czech capital looks more like dirty grey.
Welcome to the world of the panelak.
Panelaks are not exclusive to Prague - all in all, they house nearly a third of the Czech population. The first blocks were built during the 1950s and 60s to provide urgently needed housing for millions of people.
Drop in the ocean
But now the buildings are showing their age. Water leakage and drafty windows are commonplace. The insulation is in need of replacement, and in some buildings the metal skeleton within the prefabricated concrete panels is rusting away.
Housing co-operatives and the Czech Government are putting in $135m towards refurbishing the panelaks. But that's just a drop in the ocean.
Ivan Prikryl, lawyer for one of the largest unions of housing co-operatives, estimates the total amount needed is 100 times that.
Panelaks are a far cry from the stereotype of Golden Prague
The Czech Republic will join the European Union next year, and Mr Prikryl is backing moves to get EU money to fix up the panelaks. He wants the EU to change the rules for its structural funds.
"These buildings will have to be repaired within 20 years. Without more investment, the panelaks will simply collapse. People already know this," he says.
Many of the flats inside belie their drab exterior.
'Not very considerate'
The Burian family live in a panelak flat in the Prague suburb of Bohnice. It boasts a new kitchen and bathroom, shiny laminate floors and freshly painted walls - the family have invested time and money in fixing up their flat.
Nonetheless, the Burians would move elsewhere if they could afford it.
"The problem is that some people don't keep the building in good order," says Jan Burian. "They're not very considerate. That's the main problem."
He says when the panelaks were built, the Communists put everyone in together - from different communities, different parts of the country, different walks of life - "even convicts", he says.
But as an attempt at social engineering, it failed. Mr Burian says the lack of any real sense of community meant that no-one felt responsible for the upkeep of the building itself.
Shared areas have became run-down, although the panelaks have largely escaped the problems of crime which blight tower block estates in London or Paris.
'Not an investment'
But for families like the Burians, there are few options.
House prices in Prague are booming, fuelled by a buyers' belief that the Czech economy will surge ahead when the country joins the EU next year.
Estate agents' windows give the details of expensive flats in the city centre. Most panelak flats are still owned by housing co-operatives and subject to rent controls.
"Panelak flats are affordable housing, for living in now," says estate agent Michal Malecha. "But as an investment, definitely not."
Much of Prague's reputation as a tourist destination rests on its historic architecture. But for its citizens, buildings like the humble panelaks are of just as much concern.
Czechs have just voted convincingly to join the European Union. They will be waiting to see whether their hopes - and expectations - are justified.