Learn Hardcore Greek: Μερικοί ηλικιωμένοι έρχονται στον πεζόδρομο μόνο για να βλέπουν κόσμο, εκτός αν βρέχει δυνατά. - Some elderly people come to the pedestrian street just to watch people, unless it is raining heavily.

Μερικοί ηλικιωμένοι = some elderly people.
You do not use an article here (no οι) because μερικοί already makes the noun indefinite, like English some:
- μερικοί άνθρωποι = some people
- κάποιοι άνθρωποι = some people (very similar)
- οι άνθρωποι = the people (all / a specific group)

So μερικοί ηλικιωμένοι is indefinite and general, not “the elderly people” in a specific group.

What nuance does ηλικιωμένοι have compared to words like γέροι?

Ηλικιωμένοι is the polite, neutral word for elderly people / senior citizens.

ηλικιωμένος = elderly (polite, respectful)
γέρος = old man (can sound rude or dismissive, like “old geezer” depending on tone)
γριά = old woman (also often sounds rude or old-fashioned)

So μερικοί ηλικιωμένοι sounds neutral and respectful, unlike μερικοί γέροι, which could sound harsh or impolite in many contexts.

Why is έρχονται used here, and how should I understand its tense/aspect?

Έρχονται is present tense, 3rd person plural of έρχομαι = they come.

Here it expresses a habitual action (something they do regularly):

Μερικοί ηλικιωμένοι έρχονται στον πεζόδρομο...
= Some elderly people (regularly) come to the pedestrian street...

In Greek, the simple present often covers:

English they come (general / repeated)
English they are coming (right now), depending on context.

Here, because of the meaning of the whole sentence, it clearly refers to a regular habit, not a one-time event.

Why is it στον πεζόδρομο and not something else like στο πεζόδρομο or σε έναν πεζόδρομο?

Στον = σε + τον (to the / in the – masculine singular).

ο πεζόδρομος = the pedestrian street
στον πεζόδρομο = to the pedestrian street / on the pedestrian street

Points to notice:

στον vs στο
- στον is used before masculine singular nouns (τον).
- στο is used before neuter singular nouns (το).
  πεζόδρομος is masculine, so: στον πεζόδρομο, not στο πεζόδρομο.
Why not σε έναν πεζόδρομο?
- σε έναν πεζόδρομο = to a pedestrian street (any one, non-specific).
- στον πεζόδρομο usually suggests a specific or known one, or “the” pedestrian street in that town (like the main one everyone knows).

How does μόνο work in έρχονται στον πεζόδρομο μόνο για να βλέπουν κόσμο? Could it go somewhere else?

Μόνο means only and here it limits the purpose of coming:

μόνο για να βλέπουν κόσμο = only in order to watch people / just to see people

You can move μόνο a bit, but you must keep the meaning clear:

Έρχονται στον πεζόδρομο μόνο για να βλέπουν κόσμο.
Focus: they come there only for that purpose (not for coffee, shopping, etc.).
Έρχονται μόνο στον πεζόδρομο για να βλέπουν κόσμο.
Now it sounds more like: they only go to the pedestrian street (not to other places) in order to see people.

So the position of μόνο changes what is limited:

Before για να → limits the purpose.
Before στον πεζόδρομο or έρχονται → can limit the place or the action more generally.

What does για να mean in για να βλέπουν κόσμο? Is this like an infinitive?

Yes, για να + verb often corresponds to English to / in order to + verb.

για να βλέπουν = (in order) to watch / to see

Greek has no true infinitive like “to see”. Instead it uses να + verb in the subjunctive:

να βλέπω = (to) see / watch (imperfective)
να δω = (to) see (perfective)

Για να + να-verb expresses purpose:

Πάω στο σούπερ μάρκετ για να αγοράσω ψωμί.
I go to the supermarket to buy bread.
Έρχονται στον πεζόδρομο για να βλέπουν κόσμο.
They come to the pedestrian street to see people.

Why is βλέπουν used here and not δουν? What’s the difference?

Βλέπουν and δουν are different aspects of the verb “see”:

βλέπουν (from βλέπω) = imperfective (ongoing, repeated, habitual)
δουν (from βλέπω, perfective stem) = perfective (single, complete event)

In για να βλέπουν κόσμο:

βλέπουν suggests continual or repeated watching:
they come there in order to spend time watching people, to “people-watch”.
για να δουν κόσμο would suggest more a single act of seeing:
they come there in order to see people (at least once / just see them).

Here the sentence describes a habitual activity (they sit there and watch people coming and going), so the imperfective βλέπουν is more natural.

What exactly does κόσμο mean here? Why is it translated as “people” and not “world”?

Κόσμος has two main meanings:

world / universe
- ο κόσμος = the world
people / crowd / folks (very common, especially in the singular)
- Είχε πολύ κόσμο. = There were a lot of people.
- Πήγα σε ένα μέρος με πολύ κόσμο. = I went to a place with a lot of people.

In this sentence, βλέπουν κόσμο clearly uses the “people” meaning:

They come there in order to see people / watch people.

So κόσμο here = people, folks, passers-by, not “world”.

How does εκτός αν work? Is it the same as εκτός από or αν δεν?

Εκτός αν means unless (literally: except if).

εκτός αν βρέχει δυνατά = unless it’s raining hard

Compare:

εκτός αν = unless
- Θα βγω, εκτός αν βρέχει. = I’ll go out, unless it’s raining.
εκτός από = except (for) / apart from
- Μου αρέσουν όλα, εκτός από αυτό. = I like everything except this.
αν δεν = if not
- Θα βγω, αν δεν βρέχει. = I’ll go out, if it’s not raining.

Often εκτός αν and αν δεν end up close in meaning, but εκτός αν presents the rainy situation as an exception to the usual habit:

They come to the pedestrian street; the only exception is when it rains hard.

What is the structure of βρέχει δυνατά? Who is the subject of βρέχει?

Βρέχει is an impersonal verb: it means it is raining.

Greek doesn’t use a separate “dummy” subject like English it here.
So βρέχει literally is just rains, but it corresponds to it rains / it is raining.

In βρέχει δυνατά:

βρέχει = it is raining
δυνατά = strongly, hard (adverb)

So the whole phrase is: it is raining hard / it’s raining heavily.

There is no explicit subject word in Greek; the subject is just understood from the verb form (impersonal).

What does δυνατά mean here, and how is it different from πολύ?

Δυνατά is an adverb from δυνατός = strong.

In βρέχει δυνατά, it means strongly / heavily:

βρέχει δυνατά = it’s raining hard / heavily
βρέχει πολύ = it’s raining a lot / very much

They are close in meaning here; often both are possible. Very roughly:

δυνατά focuses more on intensity / force (strong rain).
πολύ focuses more on quantity / degree (a lot of rain).

In everyday speech:

Βρέχει πολύ. and Βρέχει δυνατά. are both natural, with a small nuance difference.

Could the sentence also be written as Μερικοί ηλικιωμένοι πηγαίνουν στον πεζόδρομο... instead of έρχονται? Would that change the meaning?

You could say πηγαίνουν, but there’s a nuance:

έρχονται = they come (towards the speaker’s / narrator’s place or shared reference point)
πηγαίνουν = they go (more neutral movement away from the subject’s starting point)

In context:

Έρχονται στον πεζόδρομο often implies that the πεζόδρομος is the central place for the speaker or community – like “they (come and) show up on the pedestrian street”.
Πηγαίνουν στον πεζόδρομο is more neutral: “they go to the pedestrian street”.

Meaning-wise the difference is small; both describe their habit. Έρχονται sounds a bit more like:

you are mentally “there” on that street and they come (here) to it.