Temmuz gelince sahilde akşam yürüyüşü yapmak çok keyifli.

Gelince comes from gelmek (to come) + -ince, which often means when, once, or upon.

So Temmuz gelince means something like:

• when July comes
• once July arrives
• when it becomes July

It sets up a time condition for the rest of the sentence.

Because Temmuz is the thing that is coming in this expression.

• Temmuz gelince = when July comes / when July arrives
• Temmuzda = in July

These are related, but not exactly the same.

Temmuz gelince emphasizes the arrival or start of July.
Temmuzda would simply place the action within the month of July.

So this sentence has a slightly more natural, seasonal feeling: when July arrives, evening walks on the beach are very enjoyable.

The suffix -ince / -ınca / -ünce / -unca creates a time clause meaning when or once.

Examples:

• Eve gelince = when he/she comes home
• Seni görünce = when I see you
• Yaz gelince = when summer comes

In your sentence:

• Temmuz gelince = when July comes

It is a very common way to connect two actions or states in time.

Sahilde is sahil (beach / seaside) + -de, the locative ending, meaning:

• at the beach
• on the beach
• by the seaside

So:

• sahil = beach / coast
• sahilde = at/on the beach

The locative is used because the walking happens in that location.

Because -de and -e mean different things.

• sahilde = at/on the beach → location
• sahile = to the beach → direction

Here the sentence describes where the walk takes place, not movement toward the beach. So sahilde is correct.

Akşam yürüyüşü means evening walk.

This is a common Turkish noun compound:

• akşam = evening
• yürüyüş = walk, walking, stroll
• akşam yürüyüşü = evening walk

It works like English combinations such as morning coffee, summer vacation, or evening walk.

This is because akşam yürüyüşü is an indefinite noun compound in Turkish.

In this structure:

• the first noun usually stays plain
• the second noun takes the 3rd person possessive ending

So:

• yürüyüş = walk
• akşam yürüyüşü = evening walk

This does not mean his/her evening walk here. In this pattern, the ending is just part of the noun-compound structure.

Other examples:

• elma suyu = apple juice
• yaz tatili = summer holiday
• şehir merkezi = city center

Turkish often expresses activities with a noun + yapmak pattern.

So:

• yürümek = to walk
• yürüyüş yapmak = to take a walk / to go for a walk

Both are possible, but they are not always used in exactly the same way.

• sahilde yürümek = to walk on the beach
• sahilde akşam yürüyüşü yapmak = to take an evening walk on the beach

The version with yürüyüş yapmak sounds a bit more like going for a walk as an activity.

Yapmak here means to do / to make, but in many expressions it helps form an activity phrase.

So:

• akşam yürüyüşü yapmak = to take an evening walk

This whole phrase acts like a verbal noun or infinitive phrase, and it functions as the subject of the sentence:

• Temmuz gelince sahilde akşam yürüyüşü yapmak = taking an evening walk on the beach when July comes
• çok keyifli = is very enjoyable

The -mak / -mek ending is the dictionary form of the verb, often called the infinitive.

Here it works a lot like English to walk, to take a walk, or walking in a general sense.

So:

• yapmak = to do / to make
• akşam yürüyüşü yapmak = to take an evening walk

The whole infinitive phrase can function as a noun-like unit in the sentence.

Turkish often leaves out the present-tense copula (is / are) in simple statements.

So:

• çok keyifli literally looks like very enjoyable
• but it means is very enjoyable

This is completely normal in Turkish.

So the sentence structure is basically:

• Temmuz gelince sahilde akşam yürüyüşü yapmak = taking an evening walk on the beach when July comes
• çok keyifli = is very enjoyable

Keyifli means:

• pleasant
• enjoyable
• delightful
• fun

In this sentence, çok keyifli means very enjoyable or very pleasant.

It gives the feeling that this activity is especially nice and satisfying.

Turkish usually puts the main predicate at the end.

Here the sentence is arranged like this:

• Temmuz gelince = when July comes
• sahilde = on the beach
• akşam yürüyüşü yapmak = to take an evening walk
• çok keyifli = is very enjoyable

So Turkish first gives the time and setting, then the activity, and finally the evaluation.

This is very natural Turkish word order.

It is fairly general. It means something like:

• when July comes
• once July arrives
• when it gets to be July

It does not refer to one single specific July unless the context makes that clear. It often has a habitual or seasonal meaning, like saying:

• When July comes, evening walks on the beach are very enjoyable.

So it can describe a recurring experience or a generally true feeling.

Yes. For example:

• Temmuzda sahilde akşam yürüyüşü yapmak çok keyifli.
  = Taking an evening walk on the beach in July is very enjoyable.

• Temmuz gelince sahilde yürümek çok keyifli.
  = When July comes, walking on the beach is very enjoyable.

These are all natural, but the original sentence has a nice idiomatic feel:

• Temmuz gelince gives a seasonal when July arrives feeling
• akşam yürüyüşü yapmak sounds like going for an evening walk as a pleasant activity

Here akşam is part of the noun phrase akşam yürüyüşü (evening walk), not a separate adverb.

So this is not exactly:

• to walk in the evening

It is more like:

• to take an evening walk

That is why akşam appears directly before yürüyüşü and forms one expression with it.

You could use that as a rough grammar guide for yourself, but it is not natural English.

A more natural English translation would be:

• When July comes, taking an evening walk on the beach is very enjoyable.
• Once July arrives, evening walks on the beach are very pleasant.

Literal breakdowns are helpful for learning, but the final meaning should usually be expressed more naturally in English.