Wij klimmen langzaam de berg op.

Both wij and we mean we.

• we is more common in everyday speech.
• wij is a bit more formal, careful, or emphatic.
• You often see wij in writing, in teaching materials, or when the speaker wants extra stress: Wij klimmen, niet jullie.

So Wij klimmen langzaam de berg op and We klimmen langzaam de berg op are both correct.

Because the subject is wij.

In the present tense, Dutch verbs usually work like this for klimmen:

• ik klim
• jij klimt
• hij/zij/het klimt
• wij klimmen
• jullie klimmen
• zij klimmen

So with wij, you use the infinitive form: klimmen.

Langzaam is an adverb, meaning it describes how the action happens.

In a normal Dutch main clause, the finite verb usually comes in second position, and adverbs often come after it:

• Wij klimmen langzaam ...

That is a very natural word order.

You may also see other adverb placements in Dutch depending on emphasis, but for learners, subject + finite verb + adverb is a good basic pattern here.

This is one of the most important things in the sentence.

Dutch often uses a verb particle or postposition with motion expressions. Here, op belongs with the idea of moving upward:

• de berg op klimmen = to climb up the mountain

In a main clause, Dutch often splits this kind of combination:

• finite verb earlier: klimmen
• particle at the end: op

So:

• Wij klimmen ... op

This is similar to separable verbs, where part of the verb appears at the end of the clause.

Dutch often expresses movement with a noun phrase followed by a postposition:

• de trap op = up the stairs
• de heuvel af = down the hill
• het water in = into the water
• de berg op = up the mountain

So instead of putting the word like up before the noun, Dutch can put op, af, in, etc. after the noun phrase.

This pattern is very common with verbs of movement such as:

• lopen
• rennen
• klimmen
• gaan

Not in the same way that an object works in a sentence like Ik lees het boek.

In Wij klimmen langzaam de berg op, de berg op functions more like a direction/path expression: it tells you where the movement goes.

So de berg is part of the larger phrase de berg op, meaning something like up the mountain.

That is why it may feel unusual if you are expecting English-style prepositions.

Yes, but it is not exactly the same in feel.

• de berg op klimmen strongly expresses upward movement along the mountain: climb up the mountain
• op de berg klimmen can be understood more as climb onto the mountain or simply climb on the mountain, depending on context

In many situations, Dutch speakers prefer de berg op klimmen when they mean the action of ascending.

So for a learner, de berg op is the most natural pattern to remember here.

Yes. Wij klimmen is present tense.

In Dutch, the simple present often covers both:

• general/habitual actions
• actions happening now, depending on context

So Wij klimmen langzaam de berg op can mean:

• We climb up the mountain slowly
• We are climbing up the mountain slowly

If Dutch speakers want to stress that it is happening right now, they can also use:

• Wij zijn langzaam de berg aan het opklimmen

But the simple present is already very normal.

Yes, this sentence is closely related to opklimmen.

Dutch often has:

• a basic verb: klimmen
• a particle that changes or sharpens the meaning: op
• together: opklimmen

In a main clause, separable verbs split:

• Wij klimmen ... op

So this sentence can be understood through the separable-verb idea.

That said, with motion expressions like de berg op klimmen, it is also useful to think of op as expressing direction: upward.

Both ways of understanding it are helpful for learners.

Because berg is a de-word in Dutch.

You have to learn nouns with their article:

• de berg = the mountain
• plural: de bergen

There is not always a logical reason a noun is a de-word or het-word, so it is best to memorize berg together with de.

Yes, Dutch word order can shift a little for emphasis, but the basic version here is very natural:

• Wij klimmen langzaam de berg op.

Other placements may be possible in certain contexts, but they can sound more marked or require a different structure.

For most learners, the safest pattern is:

• subject + finite verb + adverb + rest + particle

So this sentence is an excellent model to copy.