W poczekalni nie było wolnego miejsca, bo każdy wagon był prawie pełny.

Because after w meaning in for a location, Polish normally uses the locative case.

• base form: poczekalnia = waiting room
• locative singular: poczekalni

So:

• w poczekalni = in the waiting room

This is a very common pattern:

• w domu = in the house
• w szkole = at school / in the school
• w poczekalni = in the waiting room

Poczekalnia means waiting room. It can be used for:

• a train station waiting room
• a doctor’s waiting room
• any general waiting area

In this sentence, because the second half mentions wagon and suggests train travel, poczekalnia is most naturally understood as a station waiting room.

Yes, essentially. Nie było is the past-tense negative form used in an existential sense, like English there wasn’t or there were not.

• było = was / there was
• nie było = was not / there wasn’t

In Polish, this kind of sentence often uses a form of być to express existence:

• Było miejsce. = There was a place / There was room.
• Nie było miejsca. = There was no place / There was no room.

So W poczekalni nie było wolnego miejsca means something like In the waiting room, there was no free place/seat/space.

Because after negated existential expressions like nie było, Polish normally uses the genitive case, not the nominative.

The basic noun phrase is:

• wolne miejsce = a free place / a free seat / free space

But after nie było, it changes to genitive:

• nie było wolnego miejsca

Here both words change:

• wolne → wolnego
• miejsce → miejsca

This is a very important Polish pattern:

• Jest kawa. = There is coffee.
• Nie ma kawy. = There is no coffee.

Similarly:

• Było wolne miejsce. = There was a free place.
• Nie było wolnego miejsca. = There was no free place.

The singular is very natural here. Nie było wolnego miejsca means there wasn’t a single free place/seat/spot.

It has a slightly stronger not even one feeling.

A plural version is also possible:

• Nie było wolnych miejsc. = There were no free places/seats.

Both are correct, but they feel a little different:

• nie było wolnego miejsca = not a single free place
• nie było wolnych miejsc = there were no free places

In English, both might simply be translated as there were no free seats/spaces.

It can cover all of those ideas depending on context.

Miejsce literally means place or spot, but in travel contexts it often means:

• a seat
• room
• available space

So in this sentence, wolne miejsce could be understood as:

• a free seat
• an empty spot
• room for someone

That is why a natural English translation might vary depending on the situation.

Because każdy means each or every, and grammatically it goes with a singular noun.

• wagon is masculine singular
• so we say każdy wagon = each/every carriage
• and the verb agrees in singular: był

So:

• każdy wagon był prawie pełny = each carriage was almost full

Even though każdy wagon refers to many wagons in meaning, grammatically it is treated as singular, just like English every carriage was.

No. In Polish, wagon usually means a railway carriage, car, or coach, not the whole train.

So:

• pociąg = train
• wagon = carriage / railcar / coach

That means the sentence is saying that each carriage was almost full, not that each train was almost full.

This is a useful vocabulary point because English wagon often suggests something different.

Prawie means almost, and pełny means full.

So:

• prawie pełny = almost full

Prawie is an adverb, and it comes before the adjective it modifies, just like English almost full.

Also notice agreement:

• wagon is masculine singular
• so the adjective is pełny

If the noun were different, the adjective would change accordingly.

Both can mean because, but they differ in style.

• bo = very common, everyday, natural
• ponieważ = more formal or more written
• gdyż = also formal/bookish in many contexts

So in normal speech, bo is the most natural choice:

• Nie było wolnego miejsca, bo każdy wagon był prawie pełny.

You could say:

• ... ponieważ każdy wagon był prawie pełny

but it would sound a bit more formal.

No, Polish word order is fairly flexible. The sentence as given is very natural, but other orders are possible.

The original:

• W poczekalni nie było wolnego miejsca, bo każdy wagon był prawie pełny.

Another possible version:

• Nie było wolnego miejsca w poczekalni, bo każdy wagon był prawie pełny.

The difference is mainly about focus and style:

• W poczekalni... puts the location first and sets the scene
• Nie było wolnego miejsca... starts with the main fact

Polish often moves elements around for emphasis, but the case endings help preserve the meaning.

Because they agree with different grammatical structures.

1. nie było wolnego miejsca

Here było is used in an existential construction, like there was not. This often appears in the neuter singular form było.

2. każdy wagon był prawie pełny

Here the verb agrees directly with the subject:

• wagon = masculine singular
• so the past tense is był

Compare:

• miejsce było wolne = the place was free
• wagon był pełny = the carriage was full

So the difference comes from grammar and agreement, not from a change in meaning of to be.