Learn Hardcore Chinese: wǒ zài gōngyuán sànbù le hěn cháng shíjiān.

But in your sentence, 在 comes right before the place noun (公园), not before the verb on its own, so it’s clearly the “at/in” use, not the progressive “am doing” use.

Also, the presence of 了 after the verb (散步了) shows this is a completed action, not a present progressive one.

2. Why do we need 在 before 公园? Why can’t we just say 我公园散步了很长时间?

In Chinese, when you want to say you do something at a place, the normal pattern is:

Subject + 在 + Place + Verb …

So:

我在公园散步了很长时间。
I walked in the park for a long time.

If you drop 在 and say 我公园散步了很长时间, 公园 stops looking like a location phrase and more like a noun directly after the subject (which makes the sentence confusing or wrong: “I–park–walked…”).

There are some special nouns of place that can directly follow the subject without 在 (like 上课, 回家), but 公园 is not one of those in this structure. So you should keep 在:

✅ 我在公园散步了很长时间。
❌ 我公园散步了很长时间。 (unnatural / wrong)

3. What does 了 mean here? Is it just “past tense”?

了 here is the verb‑suffix 了, which mainly marks completion of an action (perfective aspect), not “past tense” in the strict sense.

In 散步了很长时间:

散步 = to take a walk
散步了 = treated as a completed event
散步了很长时间 = “walked (and the walking is viewed as one completed stretch) for a long time”

Chinese does not have a tense system like English (no -ed, -s, -ing). It uses things like:

aspect markers (了, 过, 着)
time words (昨天, 现在, 明天)

to indicate time and viewpoint.

Here, 了 tells us we are talking about a specific done event of walking; the past‑time reading then comes from context + common sense (you usually don’t say “I walk for a long time” while you’re still in the middle of it, unless you add other markers).

4. Why is 了 placed after 散步 and before 很长时间? Could it go at the end of the sentence?

The pattern here is a very common one:

Subject + (在 + Place) + Verb + 了 + Duration

So:

我在公园散步了很长时间。
I walked in the park for a long time.

This pattern highlights the duration of a finished action.

You can also see 了 at the end of a sentence, but that’s a different 了 (often called sentence‑final 了), which usually expresses a change of situation or “now it has become the case that…”. For example:

我在公园散步散了很长时间了。
I’ve been walking in the park for a long time now. (implies “and it’s now already a long time / maybe I’m still walking / I feel it’s long”)

So:

Verb + 了 + Duration → completed event with that length
… + 了 (sentence‑final) → change of state / “by now … already …”

In your sentence, 了 after 散步 fits the completed action + duration structure, which is the simplest and most neutral way to say this.

5. Can we leave out 了? What would 我在公园散步很长时间 mean?

For the meaning “I walked in the park for a long time (once / on that occasion)”, you really want 了:

✅ 我在公园散步了很长时间。

If you say:

我在公园散步很长时间。

it sounds awkward for most speakers in this “single completed event” sense. Without 了, native speakers tend to reinterpret it as something like “When I walk in the park, (it’s) for a long time” (i.e. more habitual), and even then they would usually phrase it differently, for example:

我在公园散步的时间很长。
我每次在公园散步都散很长时间。

So for a clear, natural sentence about one completed period of walking, keep 了:

我在公园散步了很长时间。

6. English has “for a long time”. Why is there no “for” in Chinese?

Chinese usually doesn’t use a separate preposition like “for” to introduce a duration. Instead, the duration phrase follows the verb (often after 了):

Basic pattern:

Subject + Verb + 了 + Duration

Examples:

我等了三个小时。 – I waited for three hours.
他工作了十年。 – He worked for ten years.
我们聊了很久。 – We chatted for a long time.

Your sentence fits the same pattern, with a location added:

我在公园散步了很长时间。
I walked in the park for a long time.

So 很长时间 itself is the duration phrase, and the “for” meaning is understood from its position after the verb (with 了).

7. Can we drop 很 in 很长时间? What is the difference between 长时间 and 很长时间?

Both are possible, but they feel a bit different:

很长时间
- Literally: “very long time” / “quite a long time”.
- Very common in spoken Chinese.
- Sounds natural, a bit more emotional or subjective (“It felt long”).
长时间
- Literally: “long time / long period (of time)”.
- Feels more formal or written if used alone, often as part of a longer noun phrase:
  - 长时间的工作 – long periods of work
  - 长时间使用电脑 – using a computer for long periods

In your sentence:

我在公园散步了很长时间。 – Very natural, conversational.
我在公园散步了长时间。 – Grammatically okay but sounds a bit stiff/odd in everyday speech.

So in spoken Chinese, 你几乎 always want the 很 here: 很长时间.

8. What exactly is 很长时间 grammatically? And why don’t we use a measure word like 一段 or 个?

很长时间 is:

很 – degree adverb (“very / quite”)
长 – adjective (“long”)
时间 – noun (“time”)

Together: “a (very) long time”.

Chinese often uses bare nouns like 时间 for vague amounts without a specific measure word, especially in set phrases:

一段时间 – a (certain) period of time
很长时间 – (for) a long time
短时间 – a short time
一些时间 – some time

You could say:

一段很长的时间 – a very long period of time (more formal/literary)
很长一段时间 – a very long period (also common)

But for everyday speech, 很长时间 is shorter and more natural.

We don’t say ✗ 很长一个小时 for “a long hour”; for a specific amount you’d normally use:

一个小时 – one hour
一个多小时 – more than an hour
两个多小时 – over two hours

9. Is 散步 a verb + object? Why isn’t it 散了很长时间步 or 散步散了很长时间?

Historically, 散步 is a verb–object combination:

散 – to stroll / to scatter
步 – step(s)

So patterns like:

我散了很长时间步。
我散步散了很长时间。

are grammatically possible and you will see similar patterns with other verb–object words (like 睡觉, 游泳, 打球):

我睡觉睡了三个小时。
他游泳游了两个小时。

However, many such combinations (including 散步, 游泳, 睡觉) have become so fixed that they’re often treated like a single verb in modern speech. When that happens, speakers frequently don’t bother to repeat or split them; they just say:

我在公园散步了很长时间。
他游泳游了两个小时。 / 他游了两个小时泳。
我睡了三个小时。 (object omitted)

So:

Your sentence 我在公园散步了很长时间 is completely natural and very common.
Forms like 我在公园散步散了很长时间 are more textbook‑ish or emphatic and not necessary for normal communication.

As a learner, it’s perfectly safe and natural to treat 散步 here simply as “to take a walk” and follow the pattern:

在 + Place + 散步 + 了 + Duration

10. What’s the difference between 散步, 走路, and 走? Could we say 我在公园走路了很长时间 instead?

Yes, you could say 我在公园走路了很长时间, but the nuance is slightly different.

散步
- “to take a walk / go for a stroll”, usually leisurely, for relaxation or light exercise.
- Often what you do in a park or after dinner for health.
- Your original sentence with 散步 strongly suggests a relaxed, intentional walk for enjoyment or exercise.
走路
- Literally “walk road”; means “to walk (as a way of moving)”.
- Focuses more on the mode of transport (on foot) rather than the leisure idea.
- 我在公园走路了很长时间 can sound like “I walked on foot in the park for a long time” (maybe exercising, maybe just moving around).
走
- Very common, and often means “to leave / to go”:
  - 我走了。 – I’m leaving.
- It can mean “walk” in some contexts, but it is ambiguous without more context.

So:

我在公园散步了很长时间。 – Best if you mean “I went for a (nice) walk in the park for a long time.”
我在公园走路了很长时间。 – Grammatically fine; can sound a bit more neutral / less “leisure‑stroll” in feeling.

11. Could we use 很久 instead of 很长时间? Are they the same?

They are very close in meaning and are often interchangeable in this kind of sentence.

很久
- Adverbial: “(for) a long time”.
- Very common in spoken Chinese.
- Example: 我等了很久。 – I waited for a long time.
很长时间
- Noun phrase: “a long time / a long period (of time)”.
- Slightly more “explicitly nouny” because of 时间, but in practice very similar.

In your sentence, both are fine:

我在公园散步了很久。
我在公园散步了很长时间。

Nuance:

很久 might feel a bit more colloquial / compact.
很长时间 can sound a bit more neutral or slightly formal, or just a stylistic choice.

For everyday use, you can treat them as practically equivalent here.

12. Does 公园 mean “the park” or “a park”? Why is there no “a / the” in Chinese?

Chinese does not use articles like English “a / an / the”. Nouns like 公园 are bare; whether they are interpreted as “a park” or “the park” depends on context.

我在公园散步了很长时间。
Could be:
- “I walked in the park for a long time.” (if both speaker and listener know which park)
- “I walked in a park for a long time.” (if it’s just some park, not specified)

If you want to make it definitely specific, you can modify it:

在那个公园 – in that park
在这个公园 – in this park
在市中心的公园 – in the park downtown

If you want to make it clearly indefinite (some park, not important which one), you can say:

在一个公园 – in a park

But most of the time, Chinese just says 在公园, and the listener infers “the” or “a” from the situation.