This is the 11535th most frequent Polish word.
kamienicą
A "kamienicą" is a tenement house or townhouse, typically a multi-story residential building.
In this sentence, 'kamienicą' is used in the instrumental case to indicate the object of admiration in the context of the street walk.
Spacerowaliśmy wzdłuż ulicy, podziwiając starą kamienicą.
We walked along the street, admiring the old tenement house.
Here, 'kamienicą' also appears in the instrumental case, indicating the location of the exchanged apartment.
Zamieniliśmy mieszkanie w kamienicą na dom na wsi.
We swapped the apartment in the tenement house for a house in the countryside.
This usage of 'kamienicą' in the instrumental case relates to the atmosphere being linked to the characteristic traits of the tenement house.