Der Waggon, in dem wir gestern saßen, war fast leer, und in unserem Abteil war es angenehm ruhig.

Because in here describes a location where we were sitting, not movement into somewhere.

• in + dative = location
• in + accusative = movement/direction

So:

• in dem Waggon = in the carriage
• in den Waggon = into the carriage

Here the clause means the carriage in which we were sitting yesterday, so German uses dative, giving dem.

Also, dem is the relative pronoun referring back to der Waggon.

Both can sometimes be heard in everyday German, but in dem is more standard and precise in this sentence.

• der Waggon, in dem wir gestern saßen = the carriage in which we were sitting
• der Waggon, wo wir gestern saßen is more colloquial and is often avoided in careful written German

English often allows where, but German frequently prefers a preposition + relative pronoun when the noun requires a preposition.

So because you sit in a carriage, German naturally says in dem.

Because in dem wir gestern saßen is a relative clause, and in German subordinate clauses the conjugated verb usually goes to the end.

Main clause:

• Der Waggon war fast leer.

Relative clause:

• in dem wir gestern saßen

Inside that clause, the verb saßen goes to the end.

This is one of the most important German word-order patterns:

• main clause: verb usually in second position
• subordinate clause: verb usually at the end

dem is a relative pronoun.

It refers back to der Waggon and means something like which or that in English, but because German includes the preposition, the whole phrase is:

• in dem = in which

Why dem specifically?

• The noun it refers to is Waggon, which is masculine: der Waggon
• The preposition in takes the dative here
• Masculine/neuter dative singular relative pronoun = dem

So:

• nominative masculine: der
• accusative masculine: den
• dative masculine: dem

Because Abteil is neuter: das Abteil, and the preposition in again shows location here, so it takes the dative.

Dative singular with a neuter noun gives:

• in unserem Abteil

Breakdown:

• Abteil = neuter noun
• in = location here, so dative
• neuter dative singular after unser- = unserem

So the form is:

• nominative: unser Abteil
• accusative: unser Abteil
• dative: unserem Abteil

The es is a kind of dummy subject. German often uses es in statements about general conditions, weather, atmosphere, or how things feel.

So:

• In unserem Abteil war es angenehm ruhig.

Literally, this is something like:

• In our compartment, it was pleasantly quiet.

The es does not refer to a specific thing like the compartment. It is just the normal grammatical subject used in this kind of expression.

This is similar to English:

• It was quiet.
• It was cold.
• It was nice.

Both are possible, but the sentence begins with In unserem Abteil to emphasize the location.

German main clauses follow the verb-second rule:

• one element comes first
• the finite verb comes second

So in:

• In unserem Abteil war es angenehm ruhig

the first element is:

• In unserem Abteil

and the verb is second:

• war

Then comes:

• es angenehm ruhig

If you started with Es, that would also be grammatical:

• Es war in unserem Abteil angenehm ruhig.

But the original version focuses more naturally on the compartment itself.

ruhig means quiet or calm.

angenehm means pleasant.

Together, angenehm ruhig means:

• pleasantly quiet
• nicely quiet

Here angenehm works like an adverb modifying ruhig. It tells you what kind of quiet it was: not just silent, but pleasantly so.

So:

• ruhig = quiet
• angenehm ruhig = pleasantly quiet / agreeably quiet

Yes. fast in German often means almost, not quickly.

So:

• fast leer = almost empty / nearly empty

This is a very common source of confusion for English speakers because English fast means something completely different.

Examples:

• fast fertig = almost finished
• fast nie = almost never
• fast leer = almost empty

If you want quickly, German would usually use schnell, not fast.

Because it is a relative clause, and German normally sets off relative clauses with commas.

So:

• Der Waggon, in dem wir gestern saßen, war fast leer

The relative clause gives extra information about der Waggon, so German punctuation requires commas before and after it.

This is stricter than in English. In German, these commas are not optional.

Normally, und by itself does not always require a comma. But here the comma is already needed because the relative clause ends right before und.

Structure:

• Der Waggon, in dem wir gestern saßen, war fast leer
• und
• in unserem Abteil war es angenehm ruhig

So the comma before und is not mainly there because of und. It is there because the relative clause has to be closed off with a comma.

saßen is the simple past form of sitzen.

Principal forms:

• infinitive: sitzen = to sit
• simple past: saß / saßen
• past participle: gesessen

In this sentence:

• wir saßen = we were sitting / we sat

German often uses the simple past in writing and in more formal narrative style. In conversation, many speakers might also say:

• in dem wir gestern gesessen haben

That means the same thing here.

They refer to different parts of the train.

• der Waggon = the railway carriage / coach / car
• das Abteil = the compartment inside it

So the sentence first talks about the larger unit:

• the carriage was almost empty

Then it talks about a smaller space within it:

• our compartment was pleasantly quiet

So Abteil is not the same as Waggon; it is a section inside the carriage.

Yes, both exist, but they are not always used in exactly the same way.

• Waggon often refers specifically to a railway carriage or rail car
• Wagen is a broader word and can mean car, vehicle, cart, or carriage depending on context

In modern everyday German, especially for passenger trains, people may also say:

• der Wagen
• der Zugwagen
• or just refer to the train more generally

But Waggon is perfectly understandable and fits well in this sentence.

Yes, it could move, but the current position is very natural.

In the relative clause:

• in dem wir gestern saßen

the adverb gestern comes before the final verb saßen, which is a common placement.

You could also say:

• in dem gestern wir saßen — this sounds wrong in normal German
• in dem wir saßen gestern — possible in special contexts, but much less natural

So the normal order is:

• subject + time expression + verb
• wir gestern saßen

That is why the sentence sounds natural as written.