Describing Places: "In Which" and "On Which"
When you want to describe a property by connecting two thoughts—like "This is the bedroom" and "my brother sleeps in it"—you use the relative pronoun który (which / that).
Because you are talking about being in or on a specific location, you must use a preposition like w (in) or na (on/at), followed by the Locative case. The pronoun który changes its ending to match the gender of the noun you are describing.
Feminine Places (w której / na której)
For feminine nouns, such as sypialnia (bedroom), łazienka (bathroom), and kamienica (tenement house), the relative pronoun becomes której.
Most enclosed rooms and buildings take the preposition w (in):
| This is a spacious bedroom in which my brother sleeps. | To jest przestronna sypialnia, w której śpi mój brat. |
| We are looking for a bathroom in which there is a new bathtub. | Szukamy łazienki, w której jest nowa wanna. |
| This is the tenement house in which we bought an apartment. | To jest kamienica, w której kupiliśmy mieszkanie. |
Masculine and Neuter Places (w którym / na którym)
For masculine and neuter nouns, the relative pronoun becomes którym.
While enclosed spaces take w (like a room—pokój), open architectural features generally take na (on). This includes a balcony (balkon), a terrace (taras), and a floor level like the ground floor (parter).
Housing estates (osiedle) also take na in Polish.
| I like this room in which you can smell the forest. | Lubię ten pokój, w którym czuć las. |
| We have a beautiful terrace on which we drink coffee in the morning. | Mamy piękny taras, na którym rano pijemy kawę. |
| I bought an apartment on the ground floor on which it is very quiet. | Kupiłem mieszkanie na parterze, na którym jest bardzo cicho. |
| This is the new housing estate on which I live. | To jest nowe osiedle, na którym mieszkam. |
Note on motion versus location: If a sentence involves movement, the first half might use the Accusative case for your destination ("I am going onto the balcony"), but the relative pronoun clause describing the static location will still use the Locative ("on which my boss is"):
| I am going onto the balcony on which my boss is. | Idę na balkon, na którym jest mój szef. |