Al llegar a la cima, vimos un prado enorme y una charca al fondo.

Because al + infinitive is a very common Spanish structure meaning when, upon, or on doing something.

So:

• al llegar = when arriving / on arriving
• al entrar = when entering
• al salir = when leaving

Here, Al llegar a la cima means When we arrived at the summit or On reaching the summit.

It does not literally mean to the arriving in natural English, even though al comes from a + el in other contexts. In this structure, you should learn al + infinitive as a set pattern.

Because the verb llegar normally uses a before a destination.

Examples:

• llegar a casa = to arrive home
• llegar al hotel = to arrive at the hotel
• llegar a la cima = to reach the summit

So a is required here because la cima is the place reached.

Because these are two different uses of a.

1. al llegar
   This is the special structure al + infinitive = when/upon doing something.

2. a la cima
   This is the normal preposition a used with llegar to show destination.

Also, al is a contraction of a + el, but only with the masculine singular article el.

• a + el = al
• a + la stays a la

So:

• al llegar = fixed structure
• a la cima = because cima is feminine

Vimos is the preterite form of ver for nosotros: we saw.

The preterite is used because the sentence describes a completed event in the past: they reached the top and then saw something.

• vimos = we saw / a finished action
• veíamos = we were seeing / we used to see / ongoing or habitual background

Here, vimos fits because it refers to a specific moment: once they got to the summit, they saw the meadow and the pond.

Not usually in this sentence, unless you want a different nuance.

• vimos = we saw it at that moment
• veíamos = we were seeing / we could see / it was in view

With Al llegar a la cima, the natural choice is vimos, because it marks the new event that happened on arrival.

Compare:

• Al llegar a la cima, vimos un prado enorme...
  = When we reached the summit, we saw a huge meadow...

• Desde la cima, veíamos un prado enorme...
  = From the summit, we could see a huge meadow...

So veíamos is possible in another context, but vimos is the most natural here.

Because Spanish often leaves out subject pronouns when the verb already makes the subject clear.

• vimos already tells you it is we
• so nosotros vimos is usually unnecessary

Spanish is a pro-drop language, which means subject pronouns are often omitted unless you want emphasis, contrast, or clarity.

So:

• Vimos un prado enorme = We saw a huge meadow
• Nosotros vimos un prado enorme = We saw a huge meadow, with extra emphasis on we

Prado means meadow or grassy field, especially a natural, green area covered in grass.

Campo is broader and can mean:

• countryside
• field
• rural area
• open land

So in this sentence:

• prado gives a more specific picture: a grassy meadow
• campo would sound less precise

If the image is of a lush open grassy area near the mountain, prado is a very suitable word.

Charca usually means a pond, pool, or sometimes even a muddy puddle, depending on context.

Compared with similar words:

• charca = small body of still water, often natural and not very elegant-sounding
• estanque = pond, often man-made or ornamental
• lago = lake
• laguna = lagoon or small lake

In this sentence, una charca suggests a small pool or pond in the distance. It may sound a bit rustic or natural.

Here al fondo means something like:

• in the background
• in the distance
• at the far end

So una charca al fondo means the pond was farther back in the scene, not close to the speaker.

This expression is very common for describing location in space or in a visual scene.

Examples:

• Al fondo de la sala = at the back of the room
• Se ven montañas al fondo = you can see mountains in the distance

Spanish word order is flexible, but the most neutral order here is:

• vimos un prado enorme y una charca al fondo

This presents the things seen in a natural descriptive sequence.

You could move al fondo for stylistic reasons:

• Al llegar a la cima, vimos al fondo una charca.

That puts more focus on the location first. But the original sentence sounds smoother and more neutral.

Also, al fondo naturally attaches to una charca here, describing where the pond was.

In Spanish, adjectives usually come after the noun.

So:

• un prado enorme = a huge meadow
• una casa grande = a big house
• un libro interesante = an interesting book

That is the normal position.

Sometimes adjectives can go before the noun, but that often changes the tone or emphasis. For a straightforward description, prado enorme is the standard order.

Yes, in many contexts both can mean summit or peak, but they are not always identical in feel.

• cima = top, summit; very common and versatile
• cumbre = summit, peak; sometimes feels a bit more elevated, formal, or associated with mountains

In this sentence, la cima sounds very natural.
La cumbre could also work, but it may sound slightly more literary or specifically mountaineering-related depending on context.

Yes, in this sentence it is understood that way because the main verb is vimos, which is we saw. The subject of llegar is normally interpreted as the same subject as the main verb unless context suggests otherwise.

So the sentence naturally means:

• When we arrived at the summit, we saw...

Spanish often uses these non-finite structures without repeating the subject, and the reader links them automatically to the subject of the main clause.

Because Spanish and English organize location expressions differently.

In Spanish, al fondo is a fixed expression:

• al = a + el
• fondo = background, back, far end

So literally it is something like at the back/background, but in natural English we usually say:

• in the background
• in the distance
• at the back

You should learn al fondo as a set phrase rather than trying to translate each word one by one.

A natural English version could be:

• When we reached the summit, we saw a huge meadow and a pond in the distance.
• On reaching the top, we saw a vast meadow and a pond further back.

This is useful because it shows that Spanish structures like al llegar and al fondo often need to be translated by meaning, not word-for-word.