Learn Hardcore Russian: Мы мечтаем о поездке к морю.

With the verb мечтать (to dream/daydream), standard Russian uses the preposition о + Prepositional case: мечтать о чём? Colloquial мечтать про occurs in speech (especially with kids), but it sounds informal or nonstandard. Stick to мечтать о in neutral or correct usage.

Why is it о поездке and not о поездку?

The preposition о governs the Prepositional case, so the noun must be in Prepositional: поездка → поездке. Accusative (поездку) would be wrong after о.

What case is морю, and why is it used?

It’s Dative singular of море. The preposition к (to, toward) takes Dative, so к морю is required. Base form: море, Dative: морю.

Why к морю and not в море or на море?

к морю = movement toward the sea (to the seaside area/coastline).
в море = into the sea (physically into the water/open sea).
на море is an idiomatic destination meaning “to the seaside” (for a vacation). For holidays, Russians very often say на море.
In this sentence, к морю is correct but a bit more “geographical/locational,” while на море sounds more like “to the seaside (for a trip).”

Would Мы мечтаем о поездке на море be more idiomatic for vacations?

Yes. When people talk about going to the seaside for a holiday, на море is the default idiom: Мы мечтаем о поездке на море sounds very natural.

Can I use an infinitive instead of a noun: Мы мечтаем поехать на море?

Absolutely. Мечтать + infinitive is common for desired actions: Мы мечтаем поехать на море.

мечтать о + noun emphasizes the thing/event (a trip).
мечтать + infinitive emphasizes the action (to go).

Can I say Мы мечтаем о том, чтобы поехать на море?

Yes. О том, чтобы + infinitive is another natural pattern with мечтать: Мы мечтаем о том, чтобы поехать на море. It’s a bit more formal or explicit.

Is об поездке ever correct, or must it be о поездке?

Here it should be о поездке. Use об before words that start with a vowel sound or in a few tricky clusters for ease of pronunciation: об отдыхе, об Америке, об этом. Before поездке, the simple о is normal.

How do I pronounce and stress the key words?

мечтаем: me‑ch‑TA‑em, stress on -та- (мечта́ем).
поездке: pa‑YEZD‑ke, stress on -е́- (пое́здке).
морю: MO‑ryu, stress on мо́- (мо́рю).
Also, the preposition о is usually pronounced like [a] when unstressed before a consonant: о поездке ~ [a паездке].

What’s the difference between поездка and путешествие here?

поездка = a trip (often shorter, concrete).
путешествие = a journey/travel (can feel longer or more “travel-esque”).
Both can work, but о поездке (на море) is the most typical for a simple seaside trip.

Does мечтать mean dreaming while asleep?

No. Мечтать is to daydream or deeply wish for something. Dreaming during sleep is expressed with видеть сны or сниться (impersonal): Мне снится море = “I’m dreaming of the sea (in my sleep).”

What verb aspect is мечтаем, and is there a perfective?

Мечтаем is present tense of the imperfective мечтать (ongoing/state). The perfective помечтать means “to do some dreaming/daydream for a while”: Мы помечтали и вернулись к работе.

Which conjugation is мечтать, and what form is мечтаем?

Мечтать is a first‑conjugation verb. Мечтаем is 1st person plural, present:
я мечта́ю, ты мечта́ешь, он/она мечта́ет, мы мечта́ем, вы мечта́ете, они мечта́ют.

Could word order change, like О поездке к морю мы мечтаем?

Yes. Russian word order is flexible. О поездке к морю мы мечтаем is possible for emphasis (fronting the topic). The neutral order is the original sentence.

Is к морю stylistically different from на море?

Slightly. К морю highlights direction toward the sea/coast. На море is the set phrase for “to the seaside (as a destination),” especially for leisure. For trip plans/vacations, на море is what you’ll hear most.

Any quick alternatives that sound natural?

Мы мечтаем о поездке на море.
Мы мечтаем поехать на море.
More formal/explicit: Мы мечтаем о том, чтобы поехать на море.