Learn Hardcore Russian: Однажды мы обязательно поедем куда‑нибудь вместе. - One day we will definitely go somewhere together.

однажды – literally “once, one time.”
Often used like “one day (on one particular occasion).” It can refer to past or future, and here it sounds a bit like a storytelling or romantic “one day”.
когда‑нибудь – “someday, at some point (in the future).”
More vague and open‑ended, less like a promise.

So:

Однажды мы обязательно поедем… – “One day we definitely will (I promise / I’m sure).”
Когда‑нибудь мы поедем… – “Someday we’ll go…” (less definite, more vague).

Using обязательно with однажды makes it sound especially confident and reassuring.

What exactly does обязательно mean here? Is it like “definitely” or “necessarily”?

Обязательно is an adverb meaning:

“definitely”
“certainly”
“for sure”
“without fail”

In this sentence, it adds a promise‑like or reassuring tone:
“One day we will definitely go somewhere together.”

It does not mean “necessary” in the logical sense here. It’s about the speaker’s strong intention or confidence, not about logical necessity.

You could move it a bit in the sentence without changing the basic meaning:

Мы обязательно однажды поедем куда‑нибудь вместе.
Мы поедем куда‑нибудь вместе, обязательно. (more emotional/colloquial)

Why is it куда‑нибудь and not где‑нибудь?

In Russian:

куда? = “to where?” (direction, movement towards a place)
где? = “where?” (location, being in a place)

Since поедем is a verb of motion (we will go/travel), Russian expects a direction word: куда?

So:

поедем куда‑нибудь – “we will go/travel somewhere (to some place).”
будем где‑нибудь – “we will be somewhere (in some place).”

That’s why куда‑нибудь is correct with поедем.

What is the difference between куда‑нибудь and куда‑то?

Both are indefinite “somewhere / anywhere (to)” words, but the nuance is different:

куда‑нибудь – “to anywhere; it doesn’t matter where.”
The place is completely non‑specific and not important; the speaker doesn’t care which place.
куда‑то – “to some place; to somewhere.”
There is some specific but unknown/unspecified place in mind (or at least implied).

In this sentence:

поедем куда‑нибудь вместе suggests “we’ll go anywhere, the main thing is that we’re together.”
поедем куда‑то вместе would sound more like “we’ll go to some place together (I don’t say which).”

Why is there a hyphen in куда‑нибудь?

Words like куда‑нибудь are formed from:

a base question word or adverb (куда, когда, как, где, etc.)
plus an indefinite particle (‑нибудь, ‑то, ‑либо)

These combinations are written with a hyphen in standard Russian:

куда‑нибудь, когда‑нибудь, как‑нибудь, где‑нибудь
куда‑то, когда‑то, как‑то
куда‑либо, когда‑либо

So the hyphen is simply the correct spelling rule for these indefinite forms.

Why is the future expressed with поедем, not будем ехать or будем ездить?

Russian has aspect, and different forms give different nuances:

поедем – future of the perfective verb поехать.
Focus: one completed trip in the future, the fact that it will happen.
будем ехать – future of the imperfective process (“we will be in the process of going by transport”).
Focus: the ongoing action at a certain time, not just the fact of the trip.
будем ездить – future repeated/habitual (“we will go there regularly / from time to time”).
Focus: repetition.

In this sentence, the speaker is promising one eventual trip together, so поедем (perfective, one event) is the natural choice.

Can the word order be changed? For example: Мы однажды обязательно поедем куда‑нибудь вместе?

Yes, Russian word order is flexible, and several variants are possible and natural:

Однажды мы обязательно поедем куда‑нибудь вместе. (neutral, common)
Мы однажды обязательно поедем куда‑нибудь вместе.
Мы обязательно однажды поедем куда‑нибудь вместе.

The basic meaning remains the same. Changes in order mainly affect rhythm and emphasis, not grammar. Starting with Однажды slightly emphasizes the “one day” idea, like the beginning of a story or a reassuring promise.

Highly unusual or broken‑up orders can sound unnatural, but the ones above are fine.

What is the nuance of вместе here? How is it different from друг с другом?

вместе = “together,” in the sense of doing the same thing at the same time / in company.
друг с другом = “with each other,” emphasizing mutual interaction.

For going somewhere:

поедем куда‑нибудь вместе – “we’ll go somewhere together” (perfectly natural).
поедем куда‑нибудь друг с другом – sounds odd; you don’t really “go with each other” in Russian, you simply go together.

Друг с другом is more typical with actions like talking, playing, fighting, helping, etc.:

Они разговаривают друг с другом. – “They are talking with each other.”

Where is the stress in the words of this sentence?

Main stresses:

Одна́жды – stress on на: ad‑NAZH‑dy
мы́ – stress on мы (only one syllable)
обяза́тельно – stress on за: oby‑ZA‑ti‑el‑no (in careful speech often [aby‑ZA‑tʲelʲ‑nə])
пое́дем – stress on е́: pa‑YE‑dem
куда́‑нибудь – main stress on да́: ku‑DA‑nibudʹ
(the ни‑ part is usually unstressed or weakly stressed)
вме́сте – stress on ме́: VMYE‑ste

You can think of the rhythm as:

Одна́жды мы обяза́тельно пое́дем куда́‑нибудь вме́сте.

Can we leave out однажды or обязательно? How does that change the meaning?

Yes, and each omission slightly changes the nuance:

Without обязательно:
- Однажды мы поедем куда‑нибудь вместе.
  Still “one day we’ll go somewhere together,” but it feels less like a firm promise and more like a simple prediction or hope.
Without однажды:
- Мы обязательно поедем куда‑нибудь вместе.
  “We will definitely go somewhere together (at some point).”
  The focus is on the certainty of going together, not on the poetic “one day” feeling.
Without both:
- Мы поедем куда‑нибудь вместе.
  A neutral statement: “We’ll go somewhere together,” with no extra emotional coloring.