Zatvor je u gradu.

Because the preposition u means different things depending on whether it shows location or movement.

• u + locative = in / inside / at a place
• u + accusative = into / to a place

Here the sentence describes where the prison is, not movement, so grad changes to the locative singular:

• grad → basic form
• u gradu → in the city / in town

Compare:

• Zatvor je u gradu. = The prison is in the city.
• Idem u grad. = I’m going into town / to the city.

Gradu is in the locative singular.

The noun grad is a masculine noun, and after u when talking about location, it takes the locative case.

So:

• nominative: grad
• locative: gradu

This is a very common pattern with masculine and neuter nouns in Croatian.

Je is the 3rd person singular present tense of the verb biti (to be).

So in this sentence:

• Zatvor = prison
• je = is
• u gradu = in the city

Croatian usually does use a form of to be in sentences like this, just as English does:

• On je umoran. = He is tired.
• Kuća je velika. = The house is big.
• Zatvor je u gradu. = The prison is in the city.

Croatian does not have articles like English a and the.

So zatvor can mean:

• a prison
• the prison

Which one is meant depends on context.

Likewise, u gradu can mean in a city, in the city, or in town, depending on the situation. In many learning examples, the most natural English translation is The prison is in the city.

Yes. Croatian word order is more flexible than English word order.

The neutral order here is:

• Zatvor je u gradu.

But you may also hear:

• U gradu je zatvor.

This version puts more focus on u gradu (in the city), almost like saying There is a prison in the city or emphasizing the location.

So the meaning stays very similar, but the emphasis can shift.

Grad can mean both city and town.

Which English word fits best depends on context. Croatian does not always make the same distinction English does.

So u gradu can be translated as:

• in the city
• in town

depending on what sounds most natural in English.

U is the normal preposition for being in a city, country, room, building, etc.

So you say:

• u gradu = in the city
• u školi = at school / in the school
• u kući = in the house

You would not normally say na gradu for in the city.
The preposition na is used with some places and surfaces, but not usually with grad in this meaning.

Yes. Zatvor is a masculine noun.

A simple clue is that many Croatian masculine nouns end in a consonant in the dictionary form:

• grad = city
• zatvor = prison
• most = bridge

Because zatvor is masculine singular, the verb is also singular:

• Zatvor je ... = The prison is ...

Not literally, but in some contexts English might express a very similar idea that way.

The Croatian sentence is structurally:

• The prison is in the city.

If you specifically want There is a prison in the city, Croatian more naturally uses ima or another structure, for example:

• U gradu ima zatvor.
  or more naturally in standard usage:
• U gradu ima zatvor(a).

But Zatvor je u gradu is primarily an identifying/location sentence: it tells you where the prison is.

A simple approximate pronunciation is:

ZAHT-vor yeh oo GRAH-doo

A few notes:

• z sounds like z in zoo
• j in je sounds like English y
• u is like oo in food
• stress is not always marked in normal writing, but saying it clearly as ZA-tvor je u GRA-du will be understood

If you want to sound more natural, keep the vowels short and clear. Croatian spelling is quite phonetic, so words are usually pronounced much as they are written.