Learn Hardcore Japanese: syuumatu ni kouen de issyo ni sanposimasyou. - Let's take a walk together in the park on the weekend.

The particle に marks a specific point in time. Here, 週末に means “on the weekend.” In Japanese, you attach に to nouns that indicate when something happens (days of the week, dates, times of day, etc.).

Why is で used after 公園 instead of を or に?

The particle で indicates the location where an action takes place. Since 散歩する (“to take a walk”) describes an activity happening in a place, you say 公園で散歩しましょう (“let’s take a walk in the park”).

を would mark a direct object, which isn’t needed here because “taking a walk” isn’t acting on the park.
に marks a point of arrival or existence, not the setting of an ongoing action.

What role does 一緒に play, and why does it come before the verb?

一緒に means “together” and functions like an adverb modifying the verb. Adverbs (or adverbial phrases) typically appear before the verb they qualify. So 一緒に散歩しましょう literally means “[Let’s] walk together.”

What does the ～ましょう ending in 散歩しましょう indicate?

The form ～ましょう is the polite volitional form of a verb. It’s used to make a suggestion or invitation that includes both speaker and listener, equivalent to “let’s …” in English. Here, 散歩しましょう means “let’s take a walk.”

There’s no subject in this sentence. How do we know who is doing the walking?

Japanese often omits obvious subjects when context makes them clear. In an invitation like this, it’s understood that we (speaker + listener) are the subjects of 散歩しましょう. Adding 私たち (“we”) is possible but usually unnecessary in casual speech.

Can I switch the order of 週末に, 公園で, and 一緒に, or does it have to stay in this sequence?

Japanese generally follows the order:
1) time (when)
2) place (where)
3) manner/adverbials (how)
4) verb

So 週末に公園で一緒に散歩しましょう is the most natural flow. You can shuffle them for emphasis (e.g. 一緒に週末に公園で散歩しましょう), but it may sound less smooth or more marked.

Could I say 週末は公園で一緒に散歩しましょう using は instead of に after 週末?

Yes. 週末は makes “as for the weekend” the topic of the sentence, whereas 週末に strictly pinpoints the time.

週末は公園で一緒に散歩しましょう ⇒ “As for the weekend, let’s take a walk in the park together.” (Sets up “weekend” as the topic.)
週末に公園で一緒に散歩しましょう ⇒ “Let’s take a walk in the park together on the weekend.” (Focuses on the timing.)

Why isn’t there a を before 散歩 in 散歩しましょう? I thought noun + する verbs needed を.

Many Suru-verbs (especially those borrowed from Chinese like 散歩する, 運動する) act like single compound verbs. With these, the を is often dropped:

common: 散歩する, 運動する, 連絡する
However, you could also say 散歩をしましょう, and it wouldn’t be wrong—it’s just more wordy. In everyday speech, learners and native speakers usually omit を with these compounds.