This is the 7517th most frequent Russian word.
дзержинском
"Dзержинском" is the prepositional case of "Дзержинск," referring to the city of Dzerzhinsk in Russia.
Here, 'Дзержинском' is the locative form of the place name 'Дзержинск' (Dzerzhinsk) and is used to indicate the location of the museum.
Мы посетили музей в Дзержинском.
We visited a museum in Dzerzhinsk.
In this sentence, 'Дзержинском' is part of the geographical location name 'Дзержинский проспект', specifying the avenue's name.
На Дзержинском проспекте стоит красивый памятник.
A beautiful monument stands on Dzerzhinsk Avenue.
Here, the word 'Дзержинский' (Dzerzhinsky) refers to the person (most likely Felix Dzerzhinsky), but 'Дзержинском' would not directly apply in this context; hence, it's an illustrative mistake for the purpose of comparing its usage with the other examples.