Frente al palacio, había una estatua tan grande que mi sobrino se quedó mirándola en silencio.

Because a + el contracts to al in Spanish.

So:

• frente a el palacio → incorrect
• frente al palacio → correct

This contraction happens with a + el and de + el:

• Voy al centro = I’m going to the centre
• Vengo del mercado = I’m coming from the market

The only common exception is when El is part of a proper name:

• Voy a El Escorial = no contraction

In your sentence, el palacio is just a normal noun phrase, so al is required.

Frente a means in front of, opposite, or facing, depending on context.

So Frente al palacio means something like:

• In front of the palace
• Opposite the palace

It sets the scene at the start of the sentence.

A learner should also know that Spanish often uses both:

• frente a
• enfrente de

They can be very similar in meaning, though frente a is very common and perfectly natural here.

Había is the imperfect form of haber used in the meaning there was / there were.

So:

• había una estatua = there was a statue

This is the normal way to say that something existed or was present in a place.

Spanish uses haber for existence, not ser or estar:

• Había una estatua = There was a statue
• not Era una estatua for there was a statue
• not Estaba una estatua for there was a statue

This is about imperfect vs preterite.

• había presents the statue as part of the background scene
• hubo would sound more like there appeared / there came to be / there was suddenly

In this sentence, the statue is just part of the setting. The main event is what the nephew did. So Spanish naturally uses:

• Frente al palacio, había una estatua...

This is very common in storytelling:

• background description → imperfect
• main action/event → often preterite

That is exactly what happens here:

• había = background description
• se quedó = main event/action

Tan... que... means so... that...

So:

• tan grande que = so big that

This structure is very common:

• tan alto que no cabe = so tall that it doesn’t fit
• tan cansado que se durmió = so tired that he fell asleep
• tan bonito que me emocionó = so beautiful that it moved me

In your sentence:

• una estatua tan grande que mi sobrino...
• a statue so big that my nephew...

Yes, but it would mean something slightly different.

• muy grande = very big
• tan grande que... = so big that...

Because the sentence continues with a result clause (that my nephew...), tan... que... is the natural structure.

Compare:

• Era una estatua muy grande. = It was a very big statue.
• Era una estatua tan grande que todos se pararon a mirarla. = It was such a big statue that everyone stopped to look at it.

In Spanish, the normal way to say my nephew before the noun is:

• mi sobrino

This is the standard possessive adjective.

Spanish can also use forms like:

• un sobrino mío = a nephew of mine
• el sobrino mío = possible in some contexts, but less neutral and often more emphatic or regional in feel

So here, mi sobrino is simply the most natural choice.

Here se quedó comes from quedarse, which often means:

• to stay
• to remain
• to be left
• to end up / stop and remain in a state

In this sentence, se quedó mirándola means something like:

• he stood/stayed there looking at it
• he remained looking at it
• he stopped and kept looking at it

It suggests that he entered a state and remained in it for a moment.

This is a very common Spanish pattern:

• se quedó callado = he went quiet / he remained silent
• se quedó dormido = he fell asleep
• se quedó mirando = he stood looking / kept staring

Because quedarse and quedar are different in meaning.

• quedar can mean things like to remain, to arrange, to fit, to be located
• quedarse often means to stay, to remain, to end up in a state, or to keep oneself somewhere/in some condition

In this sentence, se quedó mirándola is a fixed and very natural expression. The se is part of the verb quedarse.

A few examples:

• Me quedé en casa = I stayed at home
• Se quedó callado = He fell silent / remained silent
• Nos quedamos mirando el mar = We stood looking at the sea

So the se is not optional here if you want this meaning.

Because object pronouns attach to the end of the gerund in Spanish.

So:

• mirándola = correct
• mirando la = incorrect in this structure

The -la is the direct object pronoun her/it, referring to la estatua.

This attachment also happens with infinitives and affirmative commands:

• quiero verla = I want to see it
• siguió mirándola = he kept looking at it
• mírala = look at it

It refers to una estatua.

Since estatua is:

• feminine
• singular

the pronoun is:

• la = it/her

So:

• mirándola = looking at it

Spanish object pronouns must agree with the noun they replace:

• el libro → lo
• la estatua → la
• los libros → los
• las estatuas → las

Because with a direct object like the statue, Spanish normally uses a direct object pronoun, not a ella.

So the natural form is:

• mirándola = looking at it

a ella would only be used for emphasis, contrast, or clarification, and even then it usually appears alongside the pronoun:

• se quedó mirándola a ella = he kept looking at her/her in particular

Also, a is not normally used before things as direct objects, unless there is some special structure. The personal a is mainly for people.

So for la estatua, la is exactly what you want.

When a pronoun is attached to a gerund, Spanish often adds a written accent to keep the original stress.

Base form:

• mirando

With pronoun:

• mirándola

Without the accent, the stress would be pronounced differently. The accent mark tells you to keep the stress where it belongs.

This also happens in forms like:

• diciéndome
• levantándose
• escribiéndolo

So the accent is there for pronunciation/stress reasons.

Both are possible in Spanish, but en silencio is much more natural here.

• en silencio = in silence / silently
• silenciosamente = silently

Spanish often prefers a simple phrase like en silencio rather than a long adverb in -mente, especially in everyday narration.

Compare:

• Se quedó mirándola en silencio. = very natural
• Se quedó mirándola silenciosamente. = grammatically possible, but less idiomatic here

So this is a good example of Spanish sounding more natural with a noun phrase than with an English-style adverb.

Because mirar means to look at, while ver means to see.

• ver is about perception: you see something
• mirar is about directing your gaze: you look at something

In the sentence, the nephew is actively gazing at the statue, so mirar is the right verb.

Compare:

• Vi una estatua = I saw a statue
• Me quedé mirando la estatua = I stood/stayed looking at the statue

Yes, the word order can be changed, but the original order is very natural.

Original:

• Frente al palacio, había una estatua tan grande que mi sobrino se quedó mirándola en silencio.

This starts with the location, which sets the scene nicely.

Spanish is flexible, so you could also say:

• Había una estatua frente al palacio...
• Mi sobrino se quedó mirándola en silencio frente al palacio...

But each version shifts the focus a little.

The original structure is common in narration because it goes:

1. place
2. background description
3. result/event

That makes it flow very naturally.

In standard Spanish, existential haber stays singular even if the noun after it is plural.

So:

• había una estatua = there was a statue
• había dos estatuas = there were two statues

Not standard:

• habían dos estatuas

You may hear habían in some regions in everyday speech, but standard grammar prefers había for existential use.

So in your sentence, había una estatua is completely straightforward and correct.

Not exactly.

Both can mean something close to he was looking at it, but the nuance is different.

• se quedó mirándola = he stopped/remained there looking at it; it highlights the resulting state
• la estuvo mirando = he was looking at it for a while; it highlights the duration of the action

So se quedó mirándola gives a stronger feeling of being transfixed or absorbed by what he saw.

That makes it especially suitable here, because the statue was so big that it caused that reaction.