Našli smo mirno mjesto uz rijeku.

Croatian past tense is usually built from:

• the l-participle of the main verb
• plus a present-tense form of biti (to be)

So:

• našli = the past participle form of naći (to find)
• smo = we are, used here as the auxiliary

Together, našli smo means we found.

So the structure is roughly:

• našli smo = found we-have

That is the normal way to form the past tense in Croatian.

Because smo is a clitic, and Croatian clitics usually go in the second position of the sentence or clause.

In this sentence:

• Našli is the first element
• smo comes right after it

So Našli smo is the normal order.

You can also get different word orders for emphasis, for example:

• Mi smo našli mirno mjesto uz rijeku. = We found a quiet place by the river.

But a sentence usually does not start with bare smo.

Because Croatian often drops subject pronouns when they are already clear from the verb form.

Here, smo already tells you the subject is we, so mi is unnecessary.

• Našli smo... = We found...
• Mi smo našli... = also We found..., but with extra emphasis on we

So the version without mi is very natural.

The participle agrees with the subject in gender and number.

• našao sam = I found (male speaker)
• našla sam = I found (female speaker)
• našli smo = we found (masculine plural or mixed group)
• našle smo = we found (all-female group)

So našli smo usually means the speakers are:

• a mixed group, or
• a group treated grammatically as masculine plural, or
• unspecified in a general example

If the group were entirely female, you would normally say našle smo.

Because mjesto is a neuter noun, and the adjective must agree with it.

• miran = calm/quiet (masculine base form)
• mirna = feminine
• mirno = neuter

Since mjesto is neuter singular, the adjective is also neuter singular:

• mirno mjesto = a quiet/calm place

So the ending -o is there because of agreement with mjesto.

Here mjesto is in the accusative singular, because it is the direct object of našli smo (we found).

However, for many inanimate neuter nouns, the accusative singular looks exactly the same as the nominative singular.

So:

• nominative: mjesto
• accusative: mjesto

That is why it appears unchanged.

Because after uz, Croatian uses the accusative case.

The noun is:

• nominative: rijeka = river
• accusative: rijeku

So:

• uz rijeku = by/along the river

The ending changes because the preposition requires the accusative.

In this sentence, uz means something like:

• by
• along
• next to

So uz rijeku means by the river or along the river.

It often suggests being positioned beside something.

Depending on context, Croatian might also use other prepositions such as pokraj, pored, or kraj, but uz is very natural when something is located alongside something else.

It can suggest both, depending on context.

With mjesto, mirno mjesto often means:

• a quiet place
• a peaceful place
• a calm place

So it is not only about sound level; it can also suggest a peaceful atmosphere.

Because Croatian has no articles like English a and the.

So mirno mjesto can mean:

• a quiet place
• the quiet place

Which one is meant depends on context.

In this sentence, without special context, English would usually translate it as a quiet place.

Yes. Naći is a perfective verb.

That means it describes a completed event: the finding was successful and reached its result.

So Našli smo mirno mjesto uz rijeku means they did find the place.

The imperfective partner is usually nalaziti or sometimes pronalaziti in certain contexts. That would be used for repeated action, ongoing action, or general ability/context, not for one completed successful finding in the same way.

So the perfective verb fits this sentence very well.

Yes, Croatian word order is fairly flexible, but different orders change the focus or emphasis.

For example:

• Našli smo mirno mjesto uz rijeku. = neutral
• Mirno mjesto smo našli uz rijeku. = emphasizes the quiet place
• Uz rijeku smo našli mirno mjesto. = emphasizes by the river
• Mi smo našli mirno mjesto uz rijeku. = emphasizes we

So the original sentence is a very natural neutral version.