Kun olen jo nukkumassa, käytävästä kuuluu askeleita.

Kun introduces a time clause meaning when (sometimes while). Finnish typically separates a subordinate clause from the main clause with a comma:

• Kun olen jo nukkumassa, = When/while I’m already (in the process of) going to sleep,
• käytävästä kuuluu askeleita. = footsteps can be heard from the hallway.

So the comma marks the boundary between the when-clause and the main clause.

olen nukkumassa is the structure olla + -massa/-mässä, which commonly expresses being in the middle of an action or being in a situation where the action is about to/ongoingly happen. It’s often like English be sleeping / be going to sleep depending on context.

• nukun = I sleep / I am sleeping (simple present; can describe a general state or current action)
• olen nukkumassa = emphasizes the process/situation: I’m (already) in bed and falling asleep / I’m in the act of sleeping

In this sentence, it strongly suggests: I’m already settling in to sleep / just about asleep.

The difference is case and meaning:

• nukkumassa (inessive, “in”) with olla: being in the state/place of doing → already sleeping / in the process of sleeping
• nukkumaan (illative, “into/to”): movement/transition to start sleeping → going to sleep (to sleep)

Compare:

• Olen nukkumassa. = I’m asleep / I’m sleeping (in progress).
• Menen nukkumaan. = I’m going to bed / I’m going to sleep.

Here, olen ...-massa fits because it describes the speaker’s ongoing state when the sound occurs.

jo means already. It signals that by that time, the speaker has already reached the “going-to-sleep / falling-asleep” stage.

Typical placements:

• Kun olen jo nukkumassa, ... (most neutral here)
• Kun olen nukkumassa jo, ... is possible but tends to sound more marked/emphatic, often used when contrasting timing.

So jo helps set the scene: it’s already late enough that I’m already dozing off.

käytävästä is elative case (ending -sta/-stä), meaning out of / from inside something. With sound verbs like kuulua (to be audible), Finnish often marks the source/location of the sound with elative:

• käytävästä kuuluu ... = ... can be heard from the hallway (from inside the hallway area)

It’s a very common pattern: [place-ELATIVE] + kuuluu + [sound].

Sometimes you can also hear -lta/-ltä (ablative) with sound sources, but it shifts the nuance slightly:

• käytävästä (elative) = from inside/within the hallway (conceptually “out of it”)
• käytävältä (ablative) = from the hallway area/surface/side (more “from that area”)

In many everyday contexts both can occur, but käytävästä kuuluu is very idiomatic when the hallway is treated like an interior space the sound comes “out of.”

In Finnish, askeleita is grammatically the subject-like element, but it’s in the partitive plural because the clause is indefinite and describes an unbounded occurrence (“some footsteps”, not a specific set).

Also, Finnish often uses this “audibility” construction instead of an agent:

• Literally: From the hallway is-heard footsteps.
• Natural English: Footsteps can be heard from the hallway.

No person is stated as “doing” the hearing; it’s presented as a general perception.

Partitive often appears with: 1) indefinite quantity (“some”) 2) ongoing/unbounded events 3) when you’re not referring to a complete, countable set

askeleita = some footsteps / (the sound of) footsteps (indefinite, not counted) askeleet (nominative plural) would sound more like the footsteps (specific ones) are audible, as if referring to a known set.

So askeleita matches the idea of hearing an unspecified amount of footstep sounds.

Yes, kuuluu is present tense (3rd person singular of kuulua). In Finnish present tense commonly covers what English expresses with either present simple or present continuous, depending on context.

Here it describes something occurring at that moment in the scene:

• ... kuuluu askeleita = ... (you) can hear footsteps / footsteps are audible.

Yes. Finnish word order is flexible and changes emphasis:

• Käytävästä kuuluu askeleita. = neutral, sets the source first (hallway → sound)
• Askeleita kuuluu käytävästä. = highlights what is heard first (footsteps → source)

Both are grammatical; the choice is about information flow and emphasis.

Finnish often omits an explicit experiencer (“I hear…”) and instead states that something is audible:

• Kuulen askeleita käytävästä. = I hear footsteps from the hallway. (explicit “I”)
• Käytävästä kuuluu askeleita. = Footsteps can be heard from the hallway. (impersonal / objective-feeling)

The given version is especially common in narration because it focuses on the sound appearing in the environment, not on the speaker as an active perceiver.