Learn Hardcore Croatian: Kad ne mogu zaspati, sanjam o dugom putovanju preko mora do malog otoka. - When I can't fall asleep, I dream about a long trip across the sea to a small island.

Both mean “when” (in the sense of whenever/when(ever), if/when).
You can usually swap them without changing the meaning:
- Kad ne mogu zaspati… = Kada ne mogu zaspati…

Kad is more common in speech and informal writing; kada can sound a bit more formal, careful, or emphatic, but the difference is small.

Why is it ne mogu zaspati and not ne mogu spavati? Don’t both mean “can’t sleep”?

Both relate to sleep, but they focus on different parts of the process:

zaspati = to fall asleep (the moment of going from awake to asleep; perfective verb)
spavati = to sleep (the ongoing state/activity of sleeping; imperfective verb)

So:

Ne mogu zaspati = I can’t fall asleep (I’m lying in bed, but I can’t drift off).
Ne mogu spavati = I can’t sleep (maybe I keep waking up, or something is bothering me, so I can’t stay asleep properly).

In your sentence, Kad ne mogu zaspati fits perfectly because it talks about that situation before you manage to fall asleep.

Both verbs are in the present tense: Kad ne mogu zaspati, sanjam…. Is that normal, even though English also uses the present simple here?

Yes, this is completely normal in Croatian.

The sentence describes a habitual situation:

Kad ne mogu zaspati – When(ever) I can’t fall asleep (on those occasions in general)
sanjam… – I dream… / I (tend to) dream…

This is parallel to English: “When I can’t fall asleep, I dream about…” – both in present simple, expressing a general pattern.

For a future meaning, Croatian normally changes the tense, e.g.:

Kad ne budem mogao zaspati, sanjat ću o…
When I can’t fall asleep (in the future), I will dream about…

Why is there a comma after zaspati?

Croatian generally uses a comma between:

a dependent clause (here: Kad ne mogu zaspati) and
the main clause (here: sanjam o dugom putovanju…),

especially when the dependent clause comes first.

So:

Kad ne mogu zaspati, sanjam o… ✅
Sanjam o… kad ne mogu zaspati. – In this order, the comma is often omitted in everyday writing, but many people still keep it:
- Sanjam o… kad ne mogu zaspati.
- Sanjam o… kad ne mogu zaspati. (comma optional here; style preference)

Why do we say sanjam o dugom putovanju and not just sanjam dugo putovanje?

There is an important difference:

sanjati o + LOCATIVE = to dream about something (to imagine, fantasize about something)
- sanjam o dugom putovanju = I dream about a long journey (in my thoughts, wishes, imagination)
sanjati + ACCUSATIVE (object) = to dream something (while sleeping), to see it in your sleep
- sanjam dugo putovanje would more likely mean I am dreaming (in my sleep) a long journey.

In your sentence, the speaker is talking about what they think/fantasize about when they can’t sleep, so sanjam o… is the natural choice.

What case is dugom putovanju, and why does it look like that?

Dugom putovanju is in the locative singular.

putovanje (journey) = neuter noun
- nominative sg: putovanje
- locative sg: (o) putovanju (about the journey)
dug (long) = adjective
- neuter nominative sg: dugo putovanje (a long journey)
- neuter locative sg: *o dugom putovanju (about a long journey)

The preposition o (about) always takes the locative case in standard Croatian, so both the noun and the adjective must be in locative:

o dugom putovanju = about a long journey

What does preko mora literally mean, and which case is mora?

Preko mora literally means “across the sea” or “over the sea”.

preko is a preposition that takes the genitive case.
more (sea) = neuter noun
- nominative sg: more
- genitive sg: mora

So:

preko mora = across the sea (genitive after preko)

Other examples with preko + genitive:

preko mosta – across the bridge
preko rijeke – across the river

Why is it do malog otoka and not something like na mali otok?

Both structures exist, but they focus on slightly different things:

do
- genitive = up to / as far as / to the vicinity or end point
- do malog otoka = to a small island, emphasizing reaching that point or going as far as that island.
- Case:
  - otok (island), masc noun
    - genitive sg: otoka
  - mali (small), masc adjective
    - genitive sg masc: malog
  - → do malog otoka
na
- accusative = onto / to (a surface or destination)
- na mali otok = to a small island, focusing on going onto the island as a place you will be on.

In your sentence, do malog otoka fits the image of a long journey ending at a small island, sort of up to that point on the map.

What case is otoka here? It ends in -a; is it feminine?

Otok is actually a masculine noun; the -a ending here is because it’s in the genitive singular, not because it’s feminine.

nominative sg: otok (an island)
genitive sg: otoka (of an island / to an island after some prepositions like do)

Many masculine nouns form their genitive singular with -a, so the ending -a does not automatically mean the noun is feminine.

Can I change the word order, for example: Kad ne mogu zaspati, o dugom putovanju preko mora do malog otoka sanjam?

Yes, Croatian word order is quite flexible. Your alternative is grammatically correct:

Kad ne mogu zaspati, o dugom putovanju preko mora do malog otoka sanjam.

However, the neutral and most natural order here is:

Kad ne mogu zaspati, sanjam o dugom putovanju preko mora do malog otoka.

Putting sanjam earlier keeps the verb closer to the subject (implied ja) and sounds more typical in everyday speech. Moving sanjam to the end can add a bit of emphasis or stylistic flavor, but it can also sound a bit literary or unusual in casual conversation.

Why is there no ja (I) before sanjam? How do we know it means I dream?

Croatian is a pro-drop language: it usually omits subject pronouns when the verb ending already shows who the subject is.

sanjam is 1st person singular present of sanjati
- (ja) sanjam = I dream

Because the ending -am clearly marks “I”, the pronoun ja is normally left out unless you want to emphasize I in contrast to someone else (e.g. Ja sanjam, a ti radiš. – I dream, and you work.).

So:

Sanjam o dugom putovanju… is the natural, normal way to say I dream about a long journey…

What is the aspect of zaspati and sanjati, and does that affect the meaning here?

In Croatian, verb aspect (perfective vs. imperfective) is very important:

zaspati – perfective
- focuses on the moment of falling asleep (completed event)
- fits with ne mogu zaspati = I can’t (manage to) fall asleep.
sanjati – imperfective
- focuses on the ongoing process/activity of dreaming
- sanjam here describes what you regularly or typically do in that situation.

So the combination in your sentence:

Kad ne mogu zaspati (can’t accomplish the act of falling asleep)
sanjam… (I engage in the ongoing activity of dreaming/fantasizing)

is exactly the natural pairing of aspects for this meaning.

Is sanjam always “I dream”, or can it also mean “I’m daydreaming / fantasizing”?

Sanjam can mean both:

dream while sleeping
- Sinoć sam sanjao čudnu priču. – Last night I dreamed a strange story.
dream / fantasize / long for something (wide awake)
- Sanjam o dugom putovanju. – I dream about a long journey (I strongly wish for it, I imagine it).

In your sentence, because you can’t fall asleep and you start imagining a journey, the second meaning (fantasizing, daydreaming in bed) is the most natural interpretation.

Could I say maštam o dugom putovanju instead of sanjam o dugom putovanju?

Yes, you could, but the nuance changes slightly:

sanjam o – can feel a bit more emotional or poetic, often used for strong wishes / longings.
maštam o – comes from mašta (imagination), and focuses more on imagining / fantasizing creatively.

So:

Kad ne mogu zaspati, maštam o dugom putovanju preko mora do malog otoka.
= When I can’t fall asleep, I imagine/fantasize about a long journey…

Both are correct; sanjam o is just more directly linked to the earlier part of the sentence (the sleep context) and sounds very natural here.