Polako se spuštamo niz stepenice.

Se is the unstressed reflexive clitic. With spuštati, it changes the meaning from lowering something to going down / descending yourself.

• Spuštamo torbu. = We are lowering the bag.
• Spuštamo se. = We are going down.

So spuštamo se is the verb expression you need here, and in the sentence it appears as se spuštamo because of normal clitic placement.

Croatian clitics like se usually stand in the second position of the clause.

So in:

Polako se spuštamo niz stepenice.

the first element is polako, and the clitic se comes right after it.

You can also hear:

Spuštamo se niz stepenice.

because then spuštamo is the first element, and se follows it.

Both are grammatical; the word order depends on sentence structure and emphasis.

Spuštamo is the 1st person plural present tense form of the imperfective verb spuštati (se).

So it means we go down / we are going down / we descend, depending on context.

The present-tense endings for this verb are:

• (ja) spuštam se
• (ti) spuštaš se
• (on/ona/ono) spušta se
• (mi) spuštamo se
• (vi) spuštate se
• (oni/one/ona) spuštaju se

Croatian uses the simple present tense for both:

• general present meaning
• ongoing action happening right now

So spuštamo se can mean:

• we go down
• we are going down

English often needs to be + -ing, but Croatian usually does not.

The verb spuštati se is imperfective, which is natural for an ongoing action such as moving down the stairs.

Its perfective partner is spustiti se.

Compare:

• Polako se spuštamo niz stepenice. = ongoing process, we are slowly going down the stairs
• Spustili smo se niz stepenice. = completed action, we went down / got down the stairs

If you are describing the action as it is happening, the imperfective form is the normal choice.

Here niz means down, especially with movement from a higher point to a lower one along a surface or line.

So:

• niz stepenice = down the stairs
• niz ulicu = down the street
• niz brdo = down the hill

It expresses direction, not just location.

After the preposition niz, Croatian uses the accusative case because there is movement in a direction.

So:

• niz stepenice = accusative plural

The noun is stepenice. In this sentence the accusative plural looks the same as the nominative plural, which is very common with inanimate nouns.

So even though the form does not visibly change, the case is still accusative because of niz.

In this sentence it is plural.

The basic singular noun is stepenica = a step.
The plural stepenice can mean:

• steps
• stairs
• staircase, depending on context

So niz stepenice literally suggests movement down the steps, but in natural English it is usually just down the stairs.

Polako means slowly. It is an adverb, so it describes how the action happens.

Here it modifies the whole action:

• Polako se spuštamo niz stepenice. = We are going down the stairs slowly.

It can also appear in slightly different positions, depending on emphasis:

• Polako se spuštamo niz stepenice.
• Spuštamo se polako niz stepenice.

The first version is very natural and puts slowly early in the sentence.

Yes, sometimes learners also meet silaziti.

For example:

• Silazimo niz stepenice.

This also means we are going down the stairs.

But spuštati se and silaziti are not always identical in every context. In this sentence, spuštamo se gives a very natural sense of physically moving downward, and polako fits it well.

No. They express different ideas:

• niz stepenice = down the stairs → direction, movement
• na stepenicama = on the stairs → location

So:

• Polako se spuštamo niz stepenice. = we are moving downward
• Stojimo na stepenicama. = we are standing on the stairs

This is an important difference in Croatian: prepositions often tell you whether something is about movement or position.

Yes, Croatian word order is flexible, but not completely free because clitics like se have placement rules.

Natural alternatives include:

• Spuštamo se polako niz stepenice.
• Niz stepenice se spuštamo polako. — possible, but more marked
• Polako niz stepenice se spuštamo. — much less natural

The original sentence sounds smooth and neutral:

Polako se spuštamo niz stepenice.

It starts with the adverb, then places the clitic correctly, then gives the direction phrase.