Hoewel het slapen in de trein vermoeiend is, vind ik reizen met de trein nog steeds prettig.

Hoewel is a subordinating conjunction, meaning although or even though.

It introduces a subordinate clause:

Hoewel het slapen in de trein vermoeiend is

Because it is a subordinate clause, Dutch changes the word order: the finite verb goes to the end of that clause.

So:

• het slapen in de trein = the subject
• vermoeiend = the description
• is = the finite verb, placed at the end

That is why you get ... vermoeiend is, not ... is vermoeiend.

Because the first clause is introduced by hoewel, and clauses introduced by subordinating conjunctions usually send the finite verb to the end in Dutch.

Compare:

• Main clause: Het slapen in de trein is vermoeiend.
• Subordinate clause: Hoewel het slapen in de trein vermoeiend is ...

This is one of the most important Dutch word-order patterns to learn.

This is because Dutch main clauses follow the V2 rule: the finite verb must be in the second position.

In this sentence, the whole hoewel-clause comes first:

Hoewel het slapen in de trein vermoeiend is, ...

That entire clause counts as position 1. So the finite verb of the main clause, vind, must come next:

..., vind ik reizen met de trein nog steeds prettig.

If the sentence started directly with the subject, you would get:

Ik vind reizen met de trein nog steeds prettig.

Here slapen is not being used as a normal verb. It is being used as a noun-like infinitive, meaning sleeping or the act of sleeping.

Dutch often uses het + infinitive for this:

• het eten = eating
• het lezen = reading
• het slapen = sleeping

So het slapen in de trein means sleeping on the train / the act of sleeping on the train.

This is very similar to how English can use sleeping as a noun-like form.

Both patterns exist in Dutch, but they are used a bit differently.

• het slapen in de trein clearly packages the activity as a noun phrase: the act of sleeping on the train
• reizen met de trein is a more general activity phrase: travelling by train

After verbs like vinden, Dutch often uses a bare infinitive naturally when talking about an activity in general:

Ik vind reizen met de trein prettig.

You could also hear het reizen met de trein, but that sounds a bit heavier or more formal here. The version without het is very natural.

Because the two phrases mean different things:

• in de trein = in the train / on the train as a location
• met de trein = by train as a means of transport

So:

• slapen in de trein = sleeping while you are in the train
• reizen met de trein = travelling by train

This is a very common Dutch distinction:

• in de auto = in the car
• met de auto = by car

English often says on the train, but Dutch usually says in de trein.

Because vermoeiend and moe do not mean the same thing.

• vermoeiend = tiring, exhausting
  
  • it describes something that causes tiredness
• moe = tired
  
  • it describes the state of a person

So:

• Het slapen in de trein is vermoeiend. = Sleeping on the train is tiring.
• Ik ben moe. = I am tired.

In this sentence, the activity is being described, so vermoeiend is the correct choice.

Nog steeds means still.

It shows that the speaker’s opinion has not changed, despite the problem mentioned in the first clause.

So the sentence means something like:

Even though sleeping on the train is tiring, I still find travelling by train pleasant.

Compared with just nog, nog steeds often sounds a bit stronger or clearer as still / even now / nevertheless still.

Dutch often uses vinden with:

subject + vinden + thing + adjective

So here:

• ik = subject
• vind = find
• reizen met de trein = the thing being judged
• prettig = the judgment: pleasant

So:

Ik vind reizen met de trein prettig.
= I find travelling by train pleasant.

This structure is very common:

• Ik vind dit boek interessant.
• Zij vindt Nederlands moeilijk.
• Wij vinden het eten lekker.

The adjective often comes near the end of the clause.

Yes, you could use other adjectives, but the nuance changes slightly.

• prettig = pleasant, agreeable
• fijn = nice, pleasant, comfortable
• leuk = fun, nice, enjoyable

In this sentence, prettig fits well because train travel is being described as something generally pleasant or comfortable, even if one part of it is tiring.

Possible alternatives:

• Ik vind reizen met de trein nog steeds fijn.
  Very natural; slightly more everyday in tone.
• Ik vind reizen met de trein nog steeds leuk.
  More like I still enjoy train travel, with a slightly more cheerful tone.

So prettig is a good neutral choice.

Yes. Hoewel and alhoewel both mean although.

In modern Dutch, hoewel is often the more common and neutral choice. Alhoewel is also correct, but may sound a little more formal or literary to some speakers.

So both are possible:

• Hoewel het slapen in de trein vermoeiend is, ...
• Alhoewel het slapen in de trein vermoeiend is, ...

The word order stays the same.

Yes. A very common alternative is to put the main clause first:

Ik vind reizen met de trein nog steeds prettig, hoewel het slapen in de trein vermoeiend is.

That means the same thing.

The difference is mostly about emphasis:

• Starting with Hoewel ... gives the contrast right away.
• Starting with Ik vind ... prettig puts the main opinion first.

Both are natural Dutch.

Because the sentence starts with a subordinate clause:

Hoewel het slapen in de trein vermoeiend is, ...

In Dutch, when a subordinate clause comes before the main clause, it is normally separated by a comma.

So the comma helps mark the boundary between:

• the hoewel-clause
• the main clause

This is standard punctuation in Dutch.