To make matters worse, the Nazis got pissed off. Any building of historical value was demolished. And minutes later, the Red Army stopped by for a 40 year visit. One of the downsides of being under Communist rule, besides Communist rule itself, was Communist architecture. Communist architecture is a concrete rectangle with some space for people.
Soviet concrete is an experiment in how little concrete one can actually use in the concrete mix.
As a result, Soviet concrete is made of a slight bit of concrete with milk added to make up for the difference. Most buildings have been shedding concrete since their birth. The rest was eaten by birds. As a result, much of Warsaw is gray, rectangular, and eaten by birds. The buildings look like they came from the 1500s, although they were built at the same time the Soviets were building Shitsville everywhere else.