Learn Hardcore Chinese: gōngyuán hěn yuǎn, wǒmen zuò dìtiě ba.

With adjectival predicates, Chinese normally doesn’t use 是. The default pattern is Subject + 很 + adjective: 公园很远.
You can say 公园是很远, but that adds contrastive emphasis, typically followed by a turn: 公园是很远，可是坐地铁很方便。 Without that contrast, 是 sounds marked.

Does 很 always mean “very” here?

Not necessarily. In simple descriptive sentences like this, 很 often functions as a neutral linker to make the adjective predicative, and it doesn’t strongly intensify. If you truly mean “very,” use context or stronger adverbs like 非常, 真的, 特别, or structures like 太…了.

Can I drop 很 and say 公园远?

In isolation, 公园远 sounds abrupt or emphatic. You can drop 很 in certain contexts, such as short answers or contrasts:

Q: 公园远不远？ A: 远。
But for a standalone statement, 公园很远 is the natural default.

What does the comma do between the two parts?

Chinese often uses a comma to link related clauses, including reason → suggestion/result. Here it’s like “(Since) the park is far, let’s …”. You could also make the link explicit: 因为公园很远，所以我们坐地铁吧。

What does the sentence-final 吧 do? How is it different from 吗?

吧 softens the tone and makes it a suggestion or proposal: “let’s…/shall we…”.
吗 turns a statement into a yes–no question. 我们坐地铁吗？ asks whether that’s the plan, not proposing it.

What changes if I remove 吧 and say 我们坐地铁?

Without 吧, it sounds more like a decision/statement of intent (“We’re taking the subway.”) rather than a suggestion. 吧 is what makes it collaborative and polite.

Does 坐 literally mean “sit”? Why use it for transport?

Yes, the basic meaning is “sit,” but by extension it means “ride/take” for seated modes of transport: 坐地铁/坐火车/坐飞机.
Be careful: 坐在地铁上 means “be sitting on/in the subway (car),” not “take the subway” as a means.

Do I need a measure word with 地铁? How do I say “one ride” or a specific line?

No measure word is needed for the general action 坐地铁. For a trip, you can say 坐一趟地铁. For a line: 坐二号线, 坐三号线.

Can I omit 我们, or use 咱们 instead?

坐地铁吧 is fine when context makes the subject obvious.
咱们 explicitly includes both speaker and listener (common in northern varieties): 咱们坐地铁吧.
我们 is sometimes ambiguous, but in suggestions it usually includes the listener.

Is 地铁 used everywhere in the Chinese-speaking world?

Mainland China commonly says 地铁. Taiwan usually says 捷运; Hong Kong says 地铁/港铁 (MTR). In all places, people will understand 地铁.

Should I say 离 to specify “far from here,” like 公园离这儿很远?

Use 离 when you want to state distance relative to a reference point: 公园离这儿很远 / 公园离我们家很远.
公园很远 is fine when the reference is understood from context.

Why is there no 了? When would 了 appear in something like this?

This is a suggestion, not a completed action or change of state, so no 了 is needed. You might see 太远了 to express an exclamatory change-of-state feeling: 公园太远了，我们坐地铁吧。

Can I say 我们坐地铁去(公园)吧? Where does 去 go?

Yes: 我们坐地铁去公园吧 = “go to the park by subway.”
Word order is [subject] + [by-what] + 去 + [destination].
Avoid 我们去公园坐地铁吧 unless you literally mean “go to the park and (there) take the subway.”

Any pronunciation/tone-sandhi tips here?

很远: third tone + third tone → pronounce as 2–3 (hén yuǎn).
我们: men is neutral tone.
吧 is neutral tone.
地铁: dì (4th) + tiě (3rd).
公园: yuán is 2nd tone; in pinyin, yu already represents ü after y, so it’s pronounced like “gyüán,” not “guan.”

Is 吧 the same as 把?

No. 吧 (neutral tone) is a sentence-final particle for suggestions/softening. 把 (bǎ, 3rd tone) introduces the disposal construction, e.g., 把门关上. They’re unrelated despite similar pinyin.

Are there other natural ways to make this suggestion?

Yes, with slightly different nuances:

我们坐地铁，好吗？/好不好？ (seeking agreement)
要不要坐地铁？ (offer a choice)
还是坐地铁吧。 / 要不(要)我们坐地铁吧。 (“had better/how about”)

What about alternatives to 很远 like 好远 or 挺远?

很远: neutral/common.
好远: colloquial, feels like “so far.”
挺远(的): fairly far, mild tone.
太远了: “too far,” strong evaluation.