Al anochecer, quiero volver al hotel antes de que empiece a llover.

Al anochecer means at nightfall, at dusk, or when evening comes.

Here, anochecer is being used as a noun-like infinitive, not as a fully conjugated verb. The verb anochecer means to get dark or to grow night.

So literally, al anochecer is something like at the becoming-night. In natural English, we say at dusk or when it gets dark.

Because al + infinitive is a common Spanish structure that means when, upon, or at the moment of doing something.

So:

• al llegar = when arriving / upon arriving
• al salir = when leaving
• al anochecer = at dusk / when night falls

Also, al is the contraction of a + el, but in this kind of expression it functions as a fixed grammatical structure.

Because in Spanish, a + el contracts to al.

So:

• a el hotel → al hotel

This contraction is required in normal Spanish, except when el is part of a proper name, such as:

• Voy a El Escorial.

But with a normal noun like hotel, you must say al hotel.

Yes. Volver here means to go back or to return.

In this sentence, quiero volver al hotel means:

• I want to go back to the hotel
• I want to return to the hotel

Spanish often uses volver where English might use either go back or return.

Use antes de que when what follows has its own subject or is treated as a separate action.

Here:

• antes de que empiece a llover = before it starts to rain

This is different from antes de + infinitive, which you use when there is no new subject:

• Antes de salir, apaga la luz. = Before leaving, turn off the light.

So:

• antes de que + verb
• antes de + infinitive

are two different patterns.

Because antes de que normally triggers the subjunctive.

Spanish uses the subjunctive here because the action after antes de que is seen as something not yet completed or anticipated, not presented as a simple fact.

So:

• antes de que empiece a llover = before it starts raining

Not:

• antes de que empieza a llover ❌

The subjunctive form of empezar here is empiece.

Empezar is a stem-changing verb: e → ie in many forms.

Present subjunctive is formed from the yo form of the present indicative:

• present indicative yo empiezo
• remove -o
• add subjunctive endings

So:

• yo empiece
• tú empieces
• él/ella/usted empiece
• nosotros empecemos
• vosotros empecéis
• ellos/ustedes empiecen

In your sentence, the subject is understood as it:

• antes de que empiece a llover = before it starts to rain

Both are possible, but they are not exactly the same in feel.

• antes de que empiece a llover = before it starts to rain
• antes de que llueva = before it rains

The version with empezar a + infinitive emphasizes the beginning of the rain. It sounds very natural when you mean you want to get somewhere before the rain starts.

So empiece a llover is slightly more specific than llueva.

Because empezar often takes a + infinitive when it means to begin to do something.

Examples:

• empiezo a estudiar = I start studying
• empezó a hablar = he/she started talking
• empiece a llover = it starts to rain

So the a belongs to the pattern empezar a + infinitive.

The subject is not stated, because with weather expressions Spanish usually leaves it implicit.

In English we say:

• before it starts to rain

That it is only a grammatical subject; it does not refer to anything real.

Spanish normally does not use a dummy subject like English it, so it simply says:

• antes de que empiece a llover

The understood meaning is before it starts raining.

No, that would sound wrong, because it would literally suggest that you are the one starting to rain.

With antes de + infinitive, the subject is usually the same as the subject of the main verb. Here, the main subject is I:

• quiero volver

So antes de empezar... would imply before I start...

But the rain is a separate event, so Spanish needs:

• antes de que empiece a llover

Yes. Spanish word order is flexible.

These are all natural:

• Al anochecer, quiero volver al hotel antes de que empiece a llover.
• Quiero volver al hotel al anochecer, antes de que empiece a llover.
• Quiero volver al hotel antes de que empiece a llover, al anochecer.

But the placement can slightly affect what is being emphasized.

Starting with Al anochecer sets the time frame first, a bit like saying As evening falls...

It is very natural, because Al anochecer is an introductory time expression.

So this is standard and clear:

• Al anochecer, quiero volver al hotel...

Without the comma, the sentence is still understandable, but the comma helps the reader hear the pause and recognize the time expression more easily.