Za miastem lubię spacerować po lesie.

Because za can take different cases depending on the meaning.

In this sentence, za miastem means outside the city / beyond the city, describing a location, not motion toward a destination. When za expresses location here, Polish uses the instrumental case.

• miasto = city
• miastem = instrumental singular of miasto

Compare:

• Jestem za miastem. = I am outside the city.
• Jadę za miasto. = I am going outside the city.

So za miastem fits because the sentence is about where the walking happens, not about going there.

Miastem is the instrumental singular form of miasto.

The basic form is:

• miasto = city

After the preposition za in the sense of behind/beyond/outside when talking about location, Polish uses the instrumental, so:

• za miastem = outside the city / beyond the city

This kind of case change is very normal in Polish. Prepositions often force a specific case.

In this sentence, za miastem is an idiomatic way to say outside the city, often with the sense of in the countryside or away from the urban area.

It does not usually mean literally behind the city in a geometrical sense. It is more like:

• beyond the city limits
• outside town
• out in the country

So it often suggests a more natural, less urban setting.

After lubić, Polish very often uses an infinitive when talking about liking to do an activity.

So:

• lubię spacerować = I like to walk / I like going for walks

This is the most natural structure here.

You can form nouns from verbs, such as spacerowanie = walking, but that is usually less natural in everyday speech in this kind of sentence. It sounds more abstract, like talking about the activity as a concept.

So:

• Lubię spacerować. = natural, common
• Lubię spacerowanie. = possible in some contexts, but less ordinary here

Not quite. Spacerować usually means to go for a walk, to stroll, or to walk for pleasure.

It is different from simply moving on foot from one place to another. For example:

• iść = to go, to be going
• chodzić = to walk, go around, go habitually
• spacerować = to stroll / take a walk

So in this sentence, the idea is not just physical walking, but walking as a pleasant activity.

This is an important difference.

• w lesie = in the forest
• po lesie = around the forest / through the forest / all over the forest, with the idea of movement within it

Because spacerować involves moving around, po lesie is very natural. It suggests walking around among the trees, not just being located in the forest.

Compare:

• Jestem w lesie. = I am in the forest.
• Spaceruję po lesie. = I am walking around in the forest.

So po emphasizes movement within an area.

Lesie is the locative singular form of las.

• las = forest
• w lesie = in the forest
• po lesie = around the forest / through the forest

After po in this meaning, Polish uses the locative case. That is why las changes to lesie.

Yes, but the meaning changes slightly.

• spacerować w lesie = to walk in the forest
• spacerować po lesie = to walk around the forest / through the forest

Both can be correct, but po lesie often sounds more dynamic and idiomatic with walking around as an activity. It highlights movement around inside the forested area.

So po lesie is especially good if you want the sense of wandering or strolling around there.

Yes, Polish word order is flexible.

This sentence begins with Za miastem to foreground the setting: outside the city. It sounds natural and helps establish the scene first.

Other possible orders include:

• Lubię spacerować po lesie za miastem.
• Po lesie za miastem lubię spacerować.

The most neutral alternative is probably:

• Lubię spacerować po lesie za miastem.

But the original version puts more emphasis on the place: As for outside the city, I like walking in the forest there.

Yes, spacerować is imperfective.

That matters because lubię usually refers to something habitual, repeated, or generally enjoyed, and imperfective verbs fit that very well.

So lubię spacerować means:

• I like walking
• I like to go for walks
• I enjoy taking walks

It refers to a general preference, not a single completed event.

Because Polish usually does not need subject pronouns when the verb form already shows who the subject is.

• lubię = I like

The ending -ę tells you it is first person singular, so ja is unnecessary unless you want emphasis.

Compare:

• Lubię spacerować. = I like walking.
• Ja lubię spacerować. = I like walking.
  This sounds more emphatic, like I like walking.

It is present tense, but in sentences like this it usually expresses a general preference or habitual liking, not only something happening right now.

So lubię spacerować po lesie means:

• I like walking in the forest
• I enjoy walking in the forest
• I generally like to take walks in the forest

It is not about one specific moment.

It can be either, depending on context.

• las = forest / woods

In English, woods can sound a bit more informal or smaller-scale, while forest can sound more standard or larger. Polish las covers both very naturally.

So po lesie could be understood as:

• through the forest
• in the woods
• around the woods

The exact English choice depends on the translation style, not on a grammatical difference in Polish.