Na pierwszą rocznicę zaręczyn chcemy pojechać nad morze.

Because na here means something like for or on the occasion of.

In Polish, na + accusative is often used when something is planned for an event, date, or occasion:

• na urodziny = for a birthday
• na święta = for Christmas / for the holidays
• na rocznicę = for an anniversary

So:

• na pierwszą rocznicę zaręczyn = for the first anniversary of the engagement / for our first engagement anniversary

You may also hear w pierwszą rocznicę zaręczyn, which means more literally on the first anniversary of the engagement. In this sentence, na suggests the trip is planned as something for that occasion.

Because after na in this meaning, Polish uses the accusative case.

The base form is:

• pierwsza rocznica = first anniversary

But in the accusative:

• pierwszą rocznicę

Both words change because pierwsza is an adjective and rocznica is a feminine noun, so they have to match.

So the pattern is:

• nominative: pierwsza rocznica
• accusative: pierwszą rocznicę

This is a very common feminine singular pattern in Polish.

Because zaręczyn is the genitive plural form of zaręczyny.

The noun zaręczyny means engagement or engagement ceremony, and it is one of those Polish nouns that is normally used only in the plural.

Its dictionary form is:

• zaręczyny

But after rocznica, Polish asks the question rocznica czego? = anniversary of what?, so the next noun goes into the genitive:

• rocznica zaręczyn = anniversary of the engagement

So:

• zaręczyny = engagement
• rocznica zaręczyn = engagement anniversary

Yes, in normal usage, zaręczyny is treated as a plural-only noun.

That means Polish speakers usually say:

• te zaręczyny = this engagement
• nasze zaręczyny = our engagement
• rocznica zaręczyn = anniversary of the engagement

You generally do not use a singular form like zaręczyna in standard everyday Polish.

English learners often find this interesting because English uses singular engagement, while Polish uses a plural form.

Chcemy pojechać means we want to go.

Here is the breakdown:

• chcemy = we want
• pojechać = to go by vehicle / to go somewhere, perfective infinitive

So the structure is:

• chcieć + infinitive = to want to do something

Why pojechać?

Because pojechać is a perfective verb, and it focuses on the trip as a completed whole event: going there, making the trip.

Compare:

• chcemy pojechać nad morze = we want to go to the seaside
• chcemy jechać nad morze = we want to be going / want to travel there

In many situations, pojechać sounds more natural when talking about a planned trip as a single event.

This is mainly about aspect, which is very important in Polish verbs.

• jechać = imperfective
  Focuses on the process, the ongoing travel, or repeated travel in context.
• pojechać = perfective
  Focuses on the trip as a complete action: setting off and going there.

Examples:

• Jadę do Krakowa. = I’m going to Kraków. / I’m traveling to Kraków.
• Pojadę do Krakowa jutro. = I’ll go to Kraków tomorrow.
• Chcemy pojechać nad morze. = We want to go to the seaside.

For learners, a useful shortcut is:

• use jechać when thinking about traveling
• use pojechać when thinking about making the trip

Because nad morze means to the seaside / to the coast, while do morza would mean into the sea or to the sea itself in a more literal sense.

In Polish:

• nad + accusative = movement to a place by the water
• nad + instrumental = being at that place by the water

So:

• jedziemy nad morze = we’re going to the seaside
• jesteśmy nad morzem = we’re at the seaside

This is a very common pattern:

• nad jezioro / nad jeziorem
• nad rzekę / nad rzeką
• nad morze / nad morzem

So nad morze is exactly what you would normally say for a holiday trip to the coast.

Literally, morze means sea, but in the phrase jechać nad morze, it usually means go to the seaside / go to the coast.

This is just how Polish commonly expresses the idea.

So although the word itself is sea, the whole phrase is understood as:

• go to the seaside
• go to the coast
• go to the beach area

If you translate it word for word as go above the sea, that would sound strange in English, but it is not strange in Polish at all.

Yes, absolutely.

Polish word order is more flexible than English word order, because cases show the grammatical relationships.

So these are all possible:

• Na pierwszą rocznicę zaręczyn chcemy pojechać nad morze.
• Chcemy pojechać nad morze na pierwszą rocznicę zaręczyn.
• Nad morze chcemy pojechać na pierwszą rocznicę zaręczyn.

The meaning stays basically the same, but the emphasis changes:

• Na pierwszą rocznicę zaręczyn... emphasizes the occasion
• Chcemy pojechać nad morze... sounds more neutral
• Nad morze chcemy pojechać... emphasizes the destination

Not exactly, though they can be very similar in many situations.

• na pierwszą rocznicę zaręczyn = for the first anniversary, as something planned for that occasion
• w pierwszą rocznicę zaręczyn = on the first anniversary, on that date/time

In your sentence, na works very naturally because the trip is being planned for that anniversary.

Compare:

• Kupili prezent na rocznicę. = They bought a present for the anniversary.
• Spotkali się w rocznicę ślubu. = They met on their wedding anniversary.

So na often feels more occasion-oriented, while w feels more time-oriented.

Normally, no. If you mean a trip to the coast or seaside, Polish strongly prefers nad morze.

• jedziemy nad morze = we’re going to the seaside

Using do morza would usually sound wrong in this context, because it suggests movement into or toward the body of water itself, not to a seaside destination.

So for travel vocabulary, it is best to memorize:

• nad morze = to the seaside
• nad jezioro = to the lake
• nad rzekę = to the river

Yes. Polish often leaves out possessive words like my, our, your, etc. when the meaning is already obvious from context.

So:

• Na pierwszą rocznicę zaręczyn chcemy pojechać nad morze.

naturally implies:

• For our first engagement anniversary, we want to go to the seaside.

If needed, you could make it explicit:

• Na pierwszą rocznicę naszych zaręczyn chcemy pojechać nad morze.

That means:

• For the first anniversary of our engagement, we want to go to the seaside.

But in many contexts, the shorter version sounds more natural.

Yes, it is a normal and natural expression.

Polish often builds this kind of phrase with:

• rocznica + genitive noun

Examples:

• rocznica ślubu = wedding anniversary
• rocznica urodzin is not standard for birthday, because Polish just says urodziny
• rocznica zaręczyn = engagement anniversary
• rocznica poznania się = anniversary of meeting each other

So rocznica zaręczyn is a very standard Polish structure.

Pierwszą is an ordinal numeral used like an adjective, meaning first.

In Polish, ordinal numerals behave like adjectives, so they change for:

• gender
• case
• number

Because rocznicę is:

• feminine
• singular
• accusative

the form has to be:

• pierwszą

Compare:

• pierwsza rocznica = nominative
• pierwszą rocznicę = accusative
• w pierwszej rocznicy = locative, if that structure were used

So even though English first does not change, Polish pierwszy / pierwsza / pierwszą / pierwszej does.

Usually, yes: jechać / pojechać originally suggests going by some means of transport rather than on foot.

In real usage, though, Polish often uses pojechać quite broadly for trips, especially vacations or journeys to another place.

Compare:

• iść / pójść = go on foot
• jechać / pojechać = go by vehicle / travel
• lecieć / polecieć = go by plane / fly

So in this sentence, pojechać nad morze suggests taking a trip there, not walking there.