Desde la colina se veía una cascada pequeña y, más abajo, el campamento junto al arroyo.

Desde means from in the sense of a starting point or viewpoint. Here it means from the hill / from the hillside vantage point.

• Desde la colina = from the hill
• De la colina would more naturally suggest of the hill or from the hill in other contexts, but not as clearly a viewing position.

So Desde la colina tells you where the scene was being viewed from.

Here se veía is an example of impersonal/passive-like se.

It means something like:

• one could see
• you could see
• there could be seen
• was visible

So:

• Desde la colina se veía... = From the hill, you could see...

It does not necessarily mean it saw itself. This is a very common use of se in Spanish to avoid naming a specific subject such as we, they, or you.

Veía is the imperfect of ver, while vio is the preterite.

Here the imperfect is used because the sentence is describing a scene or background view, not a single completed action.

• se veía = could be seen / was visible
• se vio = was seen at a specific moment

In descriptive writing, Spanish often uses the imperfect for what was visible, what the setting was like, or what used to be there.

Spanish often leaves that unspecified when it is not important.

In se veía, the sentence avoids saying exactly who saw it. English often does the same with you could see or there was.

So the focus is on the landscape, not on the observer.

Both are possible, but the position of the adjective changes the feel slightly.

• una cascada pequeña = a small waterfall, with small as a straightforward descriptive detail
• una pequeña cascada can sound a bit more subjective, literary, or emphasize the quality more

In many basic descriptive contexts, placing the adjective after the noun is the most neutral and common choice in Spanish.

Yes, una pequeña cascada is grammatically correct.

The difference is mainly nuance:

• una cascada pequeña = neutral, literal description
• una pequeña cascada = slightly more expressive or stylistically marked

In a landscape description like this, the post-noun adjective sounds very natural.

Más abajo means lower down, further down, or below that point.

It is relative to the viewpoint established by Desde la colina. So first you see the small waterfall, and lower down you see the camp by the stream.

This is a very natural way in Spanish to describe locations in a landscape.

The comma separates the two visible elements in the scene:

• una cascada pequeña
• más abajo, el campamento junto al arroyo

It helps mark más abajo as a parenthetical location phrase, meaning lower down.

Without the comma, the sentence would be harder to parse. The comma gives the sentence a more natural descriptive rhythm.

Y simply links the two things that could be seen:

• a small waterfall
• and, lower down, the camp by the stream

So the structure is:

• se veía X y Y

The phrase más abajo is inserted to tell you where the second thing was.

Because Spanish, like English, often avoids repeating a verb when it is understood.

The full idea is:

• Desde la colina se veía una cascada pequeña y, más abajo, se veía el campamento junto al arroyo.

But repeating se veía would sound heavier. So Spanish leaves it out because it is already understood from the first part.

Junto a means next to, beside, or right by.

Because a + el = al, we get:

• junto al arroyo = next to the stream

So:

• junto a el arroyo is not correct
• junto al arroyo is the required contraction

An arroyo is usually a stream, brook, or small watercourse, smaller than a río.

So:

• arroyo = stream / brook
• río = river

Using arroyo helps create a more precise image of the landscape.

Because Spanish only contracts:

• a + el = al
• de + el = del

But here:

• desde + la does not contract
• junto a + el arroyo becomes junto al arroyo

So:

• desde la colina = no contraction
• junto al arroyo = contraction required

Yes. The verb is singular because the first understood visible item is singular.

In this type of structure, Spanish often agrees with the first singular noun phrase:

• se veía una cascada pequeña y, más abajo, el campamento...

Both cascada and campamento are singular, so se veía works naturally.

If the sentence had been built around a clearly plural idea, you would expect plural agreement:

• Desde la colina se veían una cascada y varias tiendas.

Yes. A sentence like this would also be possible:

• Desde la colina podía verse una cascada pequeña y, más abajo, el campamento junto al arroyo.

That means almost the same thing: From the hill, a small waterfall and, lower down, the camp by the stream could be seen.

However, se veía sounds simpler and very natural in descriptive narrative.

It is natural in both, but it feels especially at home in narrative or descriptive writing.

Features that make it feel literary or descriptive include:

• the scenic opening Desde la colina
• the imperfect se veía
• the placement of details like más abajo and junto al arroyo

In everyday speech, a person might say something similar, but in a story or description it sounds especially smooth and natural.