Learn Hardcore Spanish (Spain): A veces sueño con viajar a una isla remota con mi familia. - Sometimes I dream of traveling to a remote island with my family.

sueño viajar is incorrect in standard Spanish.
sueño de viajar is also wrong in this meaning, except in a few fixed expressions like soñar de algo in some dialects, but that’s not standard Peninsular Spanish.

To change the structure, you’d normally use que instead of a preposition:

Sueño que viajo a una isla remota… – I dream that I travel to a remote island…

Can I also say A veces sueño que viajo a una isla remota con mi familia? Is there any difference?

Yes, that sentence is also correct.

soñar con + infinitive: Sueño con viajar…
Focuses on the idea or desire to do something; very common for wishes and plans.
soñar que + verb: Sueño que viajo…
More literally describes the content of the dream, and is especially common for dreams while sleeping.

In practice, people sometimes use soñar con + infinitive for both wishes and sleeping dreams.
In Spain, Sueño con viajar… is the most natural way to express a wish or fantasy like in your sentence.

Why is sueño in the present tense instead of something like estoy soñando?

Spanish uses the simple present a lot more than English to talk about:

habits: Siempre leo antes de dormir.
repeated or general situations: A veces sueño con viajar…

Sueño here means I (sometimes) dream / I (sometimes) fantasize in a general, habitual way.

Estoy soñando would mean I am dreaming right now (literally, at this moment, usually while you’re asleep), so it wouldn’t fit the idea of sometimes very well.

What does A veces mean exactly, and where can it go in the sentence?

A veces means sometimes or at times.

Typical placements:

A veces sueño con viajar a una isla remota… (very natural)
Sueño a veces con viajar a una isla remota… (also correct)
Sueño con viajar a una isla remota a veces. (understandable, but less common here)

At the beginning or just after the verb are the most usual in this kind of sentence.

Related expressions:

algunas veces – also sometimes, slightly more formal/explicit
a menudo – often
de vez en cuando – from time to time

Why is viajar in the infinitive here?

After a preposition in Spanish, verbs must appear in the infinitive.
In sueño con viajar, the structure is:

soñar con + infinitive

So viajar must be in the infinitive because it comes after con.

If you wanted a conjugated verb instead, you’d remove the preposition and use que:

Sueño que viajo a una isla remota.

But you can’t say sueño con viajo – that would be ungrammatical.

Why do we say viajar a una isla and not viajar en una isla?

The preposition changes the meaning:

viajar a X = to travel to a place (destination)
- viajar a una isla – travel to an island
viajar en X = to travel in/by something (location or means of transport)
- viajar en tren / en coche – travel by train / by car
- viajar en la isla could mean traveling around on the island (already there)

For a destination, Spanish uses a, so viajar a una isla remota is the correct choice.

Why is it una isla remota and not un isla remota?

Because isla is a feminine noun in Spanish.

la isla – the island
una isla – an island

The article una must agree with the feminine noun isla, and the adjective must agree as well:

una isla remota – a remote island (feminine singular)
unas islas remotas – remote islands (feminine plural)

Un isla would be incorrect because un is the masculine form of a/an.

Could I say una remota isla instead of una isla remota? Is there any difference?

You can say una remota isla, and it’s grammatically correct, but the tone changes.

una isla remota – neutral, standard, descriptive wording.
una remota isla – sounds more literary, poetic, or emphatic, like something from a story or a novel.

In everyday speech, Spanish usually puts descriptive adjectives after the noun, so una isla remota is the normal, most natural order.

Does mi familia behave as singular or plural in Spanish? Would I say mi familia es or mi familia son?

Grammatically, familia is singular in Spanish, so the standard form is:

Mi familia es grande. – My family is big.
Mi familia vive en Madrid. – My family lives in Madrid.

In some varieties of Spanish, people sometimes use plural verbs (e.g. mi familia son...) to emphasize the idea of multiple people, but in standard Spanish (including Spain) singular is preferred.

In your sentence, con mi familia is just a prepositional phrase, so there’s no verb to agree with it.

Can I omit mi and just say con familia, like English “with family”?

No, that sounds unnatural in Spanish in this context.

Spanish usually needs a possessive with familia when you mean your own family:

con mi familia – with my family
con tu familia – with your family
con su familia – with his/her/their family

Con familia without a possessive would sound vague or odd, like “with (some) family” in a very generic sense, and it’s not how you’d naturally say this in Spanish. Sometimes you can say con la familia if the specific family is clear from context, but con mi familia is the default here.

What is the difference between sueño the verb and el sueño the noun? How do I know which is which here?

They are distinguished mainly by context (and by the article):

sueño (without article) = I dream (1st person singular of soñar).
- A veces sueño con viajar… – Sometimes I dream of traveling…
el sueño (with article) = sleep / the dream (noun).
- Tengo sueño. – I’m sleepy.
- El sueño fue muy extraño. – The dream was very strange.

Both forms are written sueño with an accent on e.
In your sentence, sueño comes right after A veces and is followed by con viajar, so it must be the verb (I dream), not the noun.