Nada más llegar al hotel, tuve que deshacer la maleta antes de cenar.

In this sentence, nada más + infinitive means as soon as.

So:

• Nada más llegar al hotel = As soon as I arrived at the hotel

It is a very common Spanish structure for saying that one thing happened immediately after another.

You can think of it as:

• Nada más + verb = as soon as [doing something]
• Nada más salir = as soon as I left / we left / he left, depending on context
• Nada más terminar = as soon as I finished / finished up

This use of nada más is different from its other meaning, nothing else / only.

Because after nada más, Spanish often uses the infinitive to express as soon as doing something.

So:

• Nada más llegar al hotel... not
• Nada más llegué al hotel...

The pattern is:

• nada más + infinitive

This is a fixed, natural structure in Spanish.

If you want, you could also express the same idea in other ways, for example:

• En cuanto llegué al hotel...
• Apenas llegué al hotel...

But with nada más, the infinitive is very common and natural.

Because a + el contracts to al in Spanish.

So:

• a el hotel → al hotel

This is a mandatory contraction, just like:

• de + el → del

Examples:

• Voy al centro
• Llegamos al restaurante
• Entró al cuarto

The only major exception is when el is part of a proper name, such as:

• a El Escorial

But in normal cases like el hotel, you must use al.

Both are possible in Spanish, but they mean slightly different things.

Here, tuve que is the preterite, and it presents the obligation as a completed event at that moment:

• tuve que deshacer la maleta = I had to unpack my suitcase

It sounds like a specific thing that came up and was done in the sequence of events.

By contrast, tenía que is the imperfect, and it often suggests:

• an ongoing obligation
• background information
• something habitual or not presented as a single completed event

Compare:

• Nada más llegar al hotel, tuve que deshacer la maleta
  = As soon as I arrived, I had to unpack my suitcase.
  A one-time event in the story.

• Cuando llegaba al hotel, tenía que deshacer la maleta
  = When I arrived at the hotel, I used to have to unpack my suitcase / I would have to unpack my suitcase.
  More habitual or descriptive.

So tuve que fits the idea of a specific past sequence.

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

Here:

• tuve clearly means I had
• so yo is not necessary

Spanish is a pro-drop language, which means subject pronouns are often omitted unless needed for:

• emphasis
• contrast
• avoiding ambiguity

So:

• Tuve que deshacer la maleta = perfectly natural
• Yo tuve que deshacer la maleta = also possible, but more emphatic, like I had to unpack the suitcase

In most neutral sentences, leaving out yo sounds more natural.

Literally, deshacer means to undo.

So literally:

• deshacer la maleta = to undo the suitcase

But in natural Spanish, this expression means:

• to unpack
• to unpack your suitcase

It is a common expression.

Related expressions:

• hacer la maleta = to pack
• deshacer la maleta = to unpack

So yes, it is basically a set phrase learners should remember as a unit.

Spanish often uses the definite article (el, la, los, las) where English would use a possessive like my or your, especially when the owner is obvious from context.

Here, if the speaker says:

• tuve que deshacer la maleta

it is naturally understood as:

• I had to unpack my suitcase

because it is obvious whose suitcase we mean.

Spanish does this a lot:

• Me lavé las manos = I washed my hands
• Me duele la cabeza = My head hurts
• Se puso el abrigo = He/She put on his/her coat

You can say mi maleta if you want to emphasize possession or contrast it with someone else’s suitcase, but la maleta is very natural here.

After a preposition like de, Spanish uses the infinitive when the subject stays the same.

So:

• antes de cenar = before having dinner / before dinner

This is the normal structure:

• antes de + infinitive

Examples:

• antes de salir = before leaving
• después de comer = after eating
• sin decir nada = without saying anything

You cannot say:

• antes de cené
  because cené is a conjugated verb, and that does not work after de in this structure.

You can say:

• antes de la cena

but that means more literally before dinner as a noun phrase.
Both can work, but they are slightly different in structure:

• antes de cenar = before eating dinner
• antes de la cena = before the dinner / before dinner

In your sentence, antes de cenar sounds very natural.

It can mean both.

In English, we often say:

• to have dinner
• to eat dinner

Spanish simply uses the verb:

• cenar = to have dinner / to eat dinner

Similarly:

• desayunar = to have breakfast
• comer = to eat / to have a meal / to have lunch, depending on context

So antes de cenar is a very normal, compact way to say before dinner or before having dinner.

Yes, to some extent.

The original sentence:

• Nada más llegar al hotel, tuve que deshacer la maleta antes de cenar.

is very natural and clear.

You could also say:

• Tuve que deshacer la maleta nada más llegar al hotel, antes de cenar.

But the original order is probably better because it presents the time setting first:

1. As soon as I arrived at the hotel
2. I had to unpack
3. before dinner

Spanish often puts time expressions at the beginning of the sentence, especially in narration.

So while word order is somewhat flexible, the original version is very idiomatic.

Yes. That would also be correct and natural.

For example:

• En cuanto llegué al hotel, tuve que deshacer la maleta antes de cenar.

This also means as soon as I arrived at the hotel.

The difference is mainly structural:

• nada más llegar = nada más + infinitive
• en cuanto llegué = conjunction + conjugated verb

Both are common.
Nada más llegar can sound slightly more compact and fluid in narration.

Other similar options include:

• apenas llegué al hotel
• al llegar al hotel

But nada más llegar is an especially useful pattern to learn.

Yes, it sounds completely natural in Spain.

Nothing in the sentence is strange or especially regional. In fact:

• nada más llegar
• tuve que
• deshacer la maleta
• antes de cenar

are all very standard.

A speaker in Spain would understand and use this sentence naturally. Speakers in many other Spanish-speaking countries would also understand it perfectly well, although they might choose slightly different wording depending on personal or regional preference.

So as a learner of Spanish from Spain, this is a very good sentence to study.