Learn Hardcore Polish: W niedzielę nie idę do biura, tylko chodzę po lesie z rodziną. - On Sunday I don’t go to the office; I just walk around the forest with my family.

iść → idę = go / am going (one specific movement, one direction, one occasion)
chodzić → chodzę = go / walk (habitually, repeatedly, or in various directions)

In nie idę do biura, idę suggests a specific occasion:

W niedzielę nie idę do biura
→ This Sunday I’m not going to the office (a particular Sunday, often the coming one).

If you said:

W niedziele nie chodzę do biura
→ On Sundays I don’t go to the office (a regular habit, every Sunday).

So idę fits a one-time plan; chodzę fits a general habit. The rest of the sentence (chodzę po lesie) then describes what you generally do (or often do) in that situation.

Why does the second part use chodzę and not idę: tylko chodzę po lesie?

Here chodzę expresses a repeated or extended activity: walking around in the forest.

idę po lesie would sound like you are moving in one direction through the forest at a particular moment.
chodzę po lesie means you walk around / stroll in the forest in general, often, or for some time, not just one straight trip.

Because going for a walk in the forest is an activity you usually do for a while, chodzę po lesie is the natural choice.

What exactly does chodzę po lesie mean? Is it “in the forest” or “around the forest”?

Literally, chodzić po czymś is to walk on/over/around/in something. It depends on context:

chodzić po lesie – walk in/around the forest, moving within that area
chodzić po mieście – walk around town
chodzić po plaży – walk along/on the beach

So chodzę po lesie is best understood as I walk in the forest / I walk around the forest. It emphasizes moving within that space, not just entering it once.

Why is it po lesie and not po lasie or po lasu?

The preposition po usually takes the locative case (miejscownik).

The noun:

Nominative: las (forest)
Locative singular: lesie

So:

po lesie – in/around the forest
w lesie – in the forest (also locative)

Forms like po lasie or po lasu are incorrect; the locative of las must be lesie.

Why is it do biura and not do biuro?

The preposition do (to, into) requires the genitive case.

The noun:

Nominative: biuro (office)
Genitive singular: biura

So:

do biura – to the office
z biura – from the office (also genitive)

Do biuro would wrongly use the nominative; after do, you must switch to genitive.

Could we say idę do biura and jestem w biurze? What is the difference between do biura and w biurze?

Yes, and the pattern is very typical:

do + genitive → movement towards / into a place
- idę do biura – I’m going to the office
w + locative → location inside a place
- jestem w biurze – I am in the office

So:

nie idę do biura – I am not going to the office (not heading there)
nie jestem w biurze – I am not in the office (I’m located somewhere else)

Different prepositions, different cases, different meanings (direction vs location).

Why is it z rodziną and not just z rodzina or z rodzinę?

The preposition z meaning “with” usually takes the instrumental case.

The noun:

Nominative: rodzina (family)
Instrumental singular: rodziną

So:

z rodziną – with (my/the) family

Forms like z rodzina or z rodzinę use the wrong endings for the case; the instrumental form must be rodziną.

What’s the difference between tylko and ale here? Why tylko instead of ale?

In this sentence:

…nie idę do biura, tylko chodzę po lesie…

tylko works like “but rather” / “but instead”, correcting or replacing the first option:

I don’t go to the office, but rather I walk in the forest.

If you used ale:

…nie idę do biura, ale chodzę po lesie…

it would mean simply “but”, adding contrast, but without the strong “instead of that, I do this” flavor.

So:

tylko – not A, but (instead) B
ale – not A, but B (simple contrast)

Both are possible, but tylko highlights the replacement more strongly.

Why is there no subject pronoun ja? How do we know it means “I”?

Polish usually drops subject pronouns when the verb ending already shows the person:

idę (ending -ę) = I go / I am going
chodzę (ending -ę) = I walk / I go (habitually)

So:

W niedzielę nie idę do biura already means On Sunday I’m not going to the office. Saying Ja w niedzielę nie idę do biura is possible, but it adds emphasis on ja (I, as opposed to someone else).

Omitting ja is the default, not the exception.

Where does nie go in Polish? Why is it nie idę, not idę nie?

With verbs, nie almost always stands directly in front of the verb:

idę → nie idę – I’m not going
chodzę → nie chodzę – I don’t go / I don’t walk
pracuję → nie pracuję – I don’t work / I’m not working

Putting nie after the verb (idę nie) is ungrammatical in standard Polish. So the basic pattern is:

nie + verb: nie idę, nie chodzę, nie pracuję.

Can the word order change? For example, is Nie idę do biura w niedzielę, tylko chodzę po lesie z rodziną also correct?

Yes, Polish word order is fairly flexible, and both are grammatical:

W niedzielę nie idę do biura, tylko chodzę po lesie z rodziną.
Nie idę do biura w niedzielę, tylko chodzę po lesie z rodziną.

The difference is in emphasis:

W niedzielę at the beginning highlights time: As for Sunday, I’m not going to the office…
Nie idę do biura w niedzielę focuses first on the fact of not going to the office, then adds “on Sunday” as extra information.

Both would be easily understood in everyday speech.

Could we say W niedziele nie chodzę do biura, tylko chodzę po lesie z rodziną? What would that mean?

Yes, and it slightly changes the meaning:

W niedzielę nie idę do biura… (singular niedzielę)
→ Usually interpreted as this Sunday / on Sunday (this time) I’m not going.
W niedziele nie chodzę do biura… (plural niedziele)
→ On Sundays I don’t go to the office (as a regular habit, every Sunday).

At a beginner level, learners often start with the singular w niedzielę to talk about a specific Sunday, and the plural w niedziele (or w każdą niedzielę) to talk about all Sundays / every Sunday.