Después queremos visitar una cueva pequeña y una cascada que está detrás de la colina.

Después means afterwards, later, or then in this kind of context. It is being used to show the next step in a sequence.

So:

• Después queremos visitar... = Afterwards / Then we want to visit...

Starting with Después is very natural when telling a plan or story in order.

Queremos visitar means we want to visit.

This adds the idea of intention or plan, not just the action itself.

Compare:

• Queremos visitar una cueva... = We want / plan to visit a cave...
• Visitamos una cueva... = We visit / visited a cave... depending on context, but in this sentence it would not express the same idea of future intention.

So queremos + infinitive is a very common way to say what someone wants or plans to do.

It is built into queremos.

Spanish verbs often include the subject, so nosotros is usually omitted unless it is needed for emphasis or contrast.

• queremos = we want

So:

• (Nosotros) queremos visitar...

Both are correct, but leaving out nosotros is more natural in most situations.

Because Spanish normally uses an article with each singular count noun.

So:

• una cueva
• una cascada

Even though English can sometimes sound fine with one article covering both items, Spanish usually repeats it here.

So una cueva pequeña y una cascada is the natural structure.

In Spanish, descriptive adjectives usually come after the noun.

So the normal order is:

• una cueva pequeña = a small cave

If you say una pequeña cueva, that is also grammatical, but putting the adjective before the noun can sound a bit more literary, expressive, or subjective.

For a straightforward description, cueva pequeña is the most neutral choice.

Because pequeña has to agree with cueva, which is a feminine singular noun.

Agreement rules:

• cueva → feminine singular
• adjective must match → pequeña

The same idea applies elsewhere in the sentence:

• una cascada
• la colina

These are also feminine singular nouns.

It most naturally refers to una cascada.

So the meaning is:

• a small cave and a waterfall that is behind the hill

In other words, the relative clause que está detrás de la colina is attached to the nearest noun, cascada.

If you wanted to clearly say that both the cave and the waterfall are behind the hill, Spanish would usually rephrase the sentence.

Because Spanish uses estar for location.

Here, the waterfall is located behind the hill, so Spanish says:

• está detrás de la colina

Compare:

• está en Madrid = it is in Madrid
• está detrás de la colina = it is behind the hill

Ser is generally not used for physical location like this.

Detrás de means behind.

It is a fixed expression in Spanish, so you normally learn it as a whole phrase:

• detrás de la colina = behind the hill
• detrás de la casa = behind the house
• detrás de mí = behind me

The de is simply part of the expression. You should think of detrás de as the Spanish equivalent of behind.

The accent mark in está shows the stressed syllable and also distinguishes it from other similar-looking words.

• está = he/she/it is
• esta = this (feminine)

So the accent is important both for pronunciation and meaning.

Yes, in many contexts it could.

• Después queremos visitar...
• Luego queremos visitar...

Both can mean afterwards / then we want to visit...

However, después is often felt as a very straightforward after that marker, while luego can also mean then. In everyday speech, both are common and natural.