U zoološki vrt idemo najradije ujutro, kad nema velike gužve.

Because u can take different cases depending on whether there is movement or location.

• u + accusative = movement into/to
• u + locative = being in/at

Here, idemo means we are going, so it expresses movement toward the zoo:

• u zoološki vrt = to the zoo

If you wanted to say we are in the zoo, you would use the locative:

• u zoološkom vrtu = in the zoo

So the contrast is:

• Idemo u zoološki vrt. = We are going to the zoo.
• Smo u zoološkom vrtu. = We are in the zoo.

It actually is in the accusative singular, but for this noun phrase, the form happens to look the same as the nominative.

• zoološki vrt = nominative singular
• zoološki vrt = accusative singular

This happens because:

• vrt is a masculine inanimate noun
• masculine inanimate nouns usually have the same nominative and accusative singular
• the adjective zoološki agrees with the noun, and in this case its accusative form is also the same as the nominative

So although the form does not visibly change, the case is still accusative because of the meaning and the preposition u with motion.

It can mean either, depending on context.

Here, idemo is the 1st person plural present tense of ići (to go). In this sentence, it is best understood as a habitual present:

• Idemo najradije ujutro = We prefer to go in the morning / We like going in the morning best

So it is not necessarily about one trip happening right now. It describes a general preference or habit.

Croatian often uses the present tense this way, just like English does in sentences such as:

• We go there in the morning
• We usually go in the morning

Najradije is the superlative adverb of rado.

The sequence is:

• rado = gladly
• radije = rather / more gladly
• najradije = most gladly / preferably / best of all

In natural English, najradije often translates as:

• preferably
• most gladly
• like best

So:

• Idemo najradije ujutro literally means something like We go most gladly in the morning
• naturally: We prefer going in the morning or We like to go in the morning best

Ujutro is a fixed adverb meaning in the morning.

It is very commonly written as one word in modern standard Croatian:

• ujutro = in the morning

You should usually learn it as a set adverb, just like:

• danas = today
• sutra = tomorrow

In this sentence, ujutro works adverbially and tells us when they prefer to go.

Because after nema (there is no / there isn’t), Croatian normally uses the genitive.

The noun is:

• gužva = crowd, rush, congestion

Its genitive singular is:

• gužve

And the adjective must agree with it:

• velika gužva = a big crowd (nominative)
• velike gužve = of a big crowd / no big crowd (genitive)

So:

• nema velike gužve = there isn’t a big crowd

This is a very important pattern in Croatian:

• ima vremena = there is time
• nema vremena = there is no time
• ima problema = there is a problem / there are problems
• nema problema = there is no problem / no problem

Yes. Kad and kada both mean when.

• kad is shorter and very common in everyday speech and writing
• kada is a bit fuller or more formal, but both are standard

So these are both fine:

• ... kad nema velike gužve
• ... kada nema velike gužve

In this sentence, kad nema velike gužve is a subordinate clause meaning:

• when there isn’t a big crowd

Because kad nema velike gužve is a subordinate clause.

Croatian normally separates this kind of clause with a comma:

• U zoološki vrt idemo najradije ujutro, kad nema velike gužve.

This is very typical with clauses introduced by words like:

• kad = when
• ako = if
• jer = because
• da = that / in order to

So the comma is not optional in standard writing here.

Yes. Croatian word order is relatively flexible, and changing it usually changes emphasis, not the basic meaning.

The given sentence:

• U zoološki vrt idemo najradije ujutro, kad nema velike gužve.

puts early emphasis on the destination: to the zoo.

You could also say:

• Najradije idemo u zoološki vrt ujutro, kad nema velike gužve.
• Ujutro idemo najradije u zoološki vrt, kad nema velike gužve.

These all mean roughly the same thing, but the focus shifts slightly.

The original sentence sounds natural and smooth, especially if the speaker wants to foreground where they like to go.

It is broader than just crowd.

Gužva can mean:

• a crowd of people
• bustle
• rush
• congestion
• a busy, packed situation

So nema velike gužve does not only mean there aren’t many people. It can also suggest:

• it is not too busy
• it is not packed
• it is not crowded

That is why it fits very naturally with a place like a zoo.

In this sentence, it means in the morning, generally speaking.

Because idemo is being used habitually, the sentence expresses a general preference:

• We prefer going in the morning
• We like to go in the morning

It does not necessarily mean one particular morning unless the wider context makes that clear.

Yes. Zoološki vrt is the standard and normal expression for zoo.

Literally, it means something like:

• zoological garden

This is similar to some other European languages. In everyday Croatian, people very commonly use the full phrase:

• Idemo u zoološki vrt. = We’re going to the zoo.

You may also hear people shorten things in casual conversation if the context is obvious, but zoološki vrt is the standard form you should learn.

Yes, but the meaning would shift slightly.

Compare:

• U zoološki vrt idemo najradije ujutro...
• U zoološki vrt volimo ići ujutro...

The second version, with volimo ići, is more explicitly:

• We like to go to the zoo in the morning

The original version with idemo najradije is very natural Croatian and expresses preference in a slightly more idiomatic way:

• We go most gladly in the morning
• We prefer to go in the morning

So both are possible, but the original is a very normal Croatian way to say it.