Vimos un fantasma en la casa.

Vimos is the preterite form of ver (to see) for nosotros (we).

• ver → vimos
• It means we saw
• The preterite is used for a completed action in the past

So Vimos un fantasma en la casa presents the seeing as a finished event.

Spanish often drops subject pronouns when the verb already makes the subject clear.

• Vimos already tells you the subject is we
• So Nosotros vimos un fantasma en la casa is possible, but usually unnecessary

You might include nosotros only for:

• emphasis
• contrast
• clarity

For example:

• Nosotros vimos un fantasma, pero ellos no.

Because fantasma is a masculine noun, even though it ends in -a.

So you say:

• un fantasma
• el fantasma

This is one of those nouns whose gender does not follow the most common ending pattern.

In this sentence, la casa means the house — a specific house.

• en la casa = in the house
• en casa = at home / at someone’s home

So there is an important difference:

• Vimos un fantasma en la casa = we saw a ghost in the house
• Vimos un fantasma en casa = we saw a ghost at home

The article la makes the location feel more specific.

En is the normal preposition for in, at, or sometimes on, depending on context.

Here:

• en la casa = in the house

You do not use a here, because a usually suggests movement to a place, not location in a place.

Compare:

• Estamos en la casa = we are in the house
• Vamos a la casa = we are going to the house

Yes. Spanish word order is more flexible than English.

These are both natural:

• Vimos un fantasma en la casa
• En la casa vimos un fantasma

The difference is mainly focus:

• Vimos un fantasma en la casa: neutral order
• En la casa vimos un fantasma: puts extra attention on where it happened

The basic meaning stays the same.

Usually it can suggest both, and context normally makes it clear.

In practice, the sentence is understood as:

• the sighting happened in the house
• and the ghost was also in the house

If you needed to be more precise, Spanish can rephrase it. For example:

• Vimos un fantasma que estaba en la casa = We saw a ghost that was in the house
• Estábamos en la casa cuando vimos un fantasma = We were in the house when we saw a ghost

So the original sentence is natural, but slightly broad in exactly what en la casa attaches to.

Because the personal a is usually used with specific human direct objects, and sometimes with pets or very personified beings.

Here, un fantasma is:

• not a specific named person
• not treated like a normal human direct object

So:

• Vimos un fantasma is correct

Compare with a person:

• Vimos a María
• Vi a un hombre en la calle

With fantasma, Spanish normally does not use the personal a in this sentence.

Good question. Both are past forms, but they do different jobs.

• vimos = we saw → completed event
• veíamos = we were seeing / we used to see → ongoing, habitual, or background action

So:

• Vimos un fantasma en la casa = one completed sighting
• Veíamos sombras en la casa = we were seeing shadows / we used to see shadows

For a single clear event, vimos is the normal choice.

Yes, absolutely.

In much of Spain, the present perfect (hemos visto) is very common for past events that are still connected to the present, especially within a time period considered unfinished.

Very roughly:

• Vimos un fantasma en la casa = we saw a ghost in the house
• Hemos visto un fantasma en la casa = we have seen a ghost in the house

In Spain, hemos visto may sound especially natural if the event is recent or still relevant now. But vimos is still completely correct for a finished past event.

A simple pronunciation guide is:

BEE-mos oon fan-TAS-ma en la KA-sa

A few helpful points:

• v in Spanish is pronounced more like a soft b
• un is short, not strongly stressed
• fantasma is stressed on tas
• casa is stressed on the first syllable: KA-sa

In standard Spain pronunciation:

• the s in casa is a normal s
• there is no English-style strong aspiration

Yes. Although the basic meaning is ghost, it can also be used more figuratively in some contexts.

Depending on context, fantasma can suggest:

• a ghost or apparition
• something ghost-like
• in informal speech, sometimes even a person seen as ridiculous, showy, or fake

But in Vimos un fantasma en la casa, the default reading is definitely the literal one: a ghost.

Yes, it is natural and correct.

A native speaker could also say related versions depending on emphasis:

• Vimos un fantasma en la casa
• En la casa vimos un fantasma
• Vimos un fantasma dentro de la casa — slightly more explicit: inside the house
• Hemos visto un fantasma en la casa — also common in Spain in the right context

So the original sentence is a perfectly normal way to say it.