На морском курорте мы долго слушали прибой вечером.

Russian often uses на with places that are thought of as sites, venues, or destinations where an activity happens, and курорт is commonly one of them.

So на курорте is the normal way to say at a resort.

• на морском курорте = at a seaside resort
• в would usually suggest being inside something, and with курорт that is not the usual choice.

This is something you largely learn as a collocation:

• на курорте
• на вокзале
• на почте

while other locations take в, such as:

• в городе
• в гостинице
• в доме

Because after на meaning location, Russian uses the prepositional case.

Here:

• морской → морском
• курорт → курорте

So:

• dictionary form: морской курорт
• in the sentence: на морском курорте

The adjective has to agree with the noun in:

• case
• number
• gender

Since курорт is masculine singular in the prepositional case, морской becomes морском.

Прибой means surf, the sound of waves breaking, or waves crashing on the shore.

In this sentence, слушали прибой means listened to the surf.

Grammatically, прибой is the direct object of слушали, so it is in the accusative case. But because it is an inanimate masculine noun, its accusative singular looks the same as the nominative singular:

• nominative: прибой
• accusative: прибой

So even though the form does not change, its role in the sentence is still object.

Because слушать normally takes a direct object in Russian, just like to listen to something in English, but without a preposition.

Compare:

• слушать музыку = to listen to music
• слушать радио = to listen to the radio
• слушать прибой = to listen to the surf

This is a very important difference from English:

• English: listen to
• Russian: слушать + accusative

Слушали is the past tense plural form of слушать.

It is plural because the subject is мы = we.

In the Russian past tense:

• masculine singular: слушал
• feminine singular: слушала
• neuter singular: слушало
• plural: слушали

So:

• я слушал / я слушала
• мы слушали

Because the sentence describes an activity as ongoing / extended in time, not as a single completed event.

The word долго = for a long time strongly fits the imperfective verb слушать:

• мы долго слушали прибой = we listened to the surf for a long time

If you used послушали, it would sound more like:

• we listened for a bit / we listened and finished

That is possible in some contexts, but here the focus is on the duration and experience, so слушали is the natural choice.

Долго means for a long time.

It is an adverb, modifying the verb слушали.

So:

• мы долго слушали прибой = we listened to the surf for a long time

Russian word order is flexible, so долго can move around more than in English, but different placements can slightly change emphasis:

• Мы долго слушали прибой вечером.
• Мы слушали прибой долго вечером.
• Вечером мы долго слушали прибой.

The version in your sentence sounds natural and keeps долго closely tied to the action of listening.

Because Russian often uses the instrumental case to express time words meaning in the morning, in the evening, at night, and so on.

Here:

• вечер = evening
• вечером = in the evening

Similar examples:

• утром = in the morning
• днём = during the day
• ночью = at night

So вечером is a standard time expression, and you should learn it as a set pattern.

Yes. Russian often drops subject pronouns when they are clear from the verb form.

So both are possible:

• Мы долго слушали прибой вечером.
• Долго слушали прибой вечером.

Because слушали is plural past tense, the listener can often understand that the subject is we or they from context.

Including мы makes the subject explicit. It may sound a bit clearer or slightly more contrastive, depending on context.

Russian word order is flexible, so the sentence can begin with the place to set the scene first.

Starting with На морском курорте gives a natural setting-first structure:

• At the seaside resort, we listened to the surf for a long time in the evening.

This is very common in Russian. The speaker often puts at the beginning:

• the place
• the time
• or the most important context

The sentence could also be rearranged, for example:

• Мы долго слушали прибой вечером на морском курорте.
• Вечером мы долго слушали прибой на морском курорте.

These are all grammatical, but the original version foregrounds the location.

Yes, it is natural.

A rough information flow is:

• На морском курорте — setting
• мы — subject
• долго слушали — main action
• прибой — object
• вечером — time frame

Russian does not have one fixed word order like English, but the original sentence sounds quite normal because it moves from:

1. place,
2. to subject,
3. to action,
4. to what was listened to,
5. to time.

Putting вечером at the end can make it feel like a final detail that rounds out the scene.