Hace veinte minutos que intento descifrar el acertijo.

Because Spanish often uses the pattern hace + amount of time + que + present tense to say how long something has been happening.

So:

Hace veinte minutos que intento descifrar el acertijo
= I’ve been trying to figure out the riddle for twenty minutes

Here, hace veinte minutos does not mean twenty minutes ago by itself. In this structure, it expresses a duration that continues up to now.

Because the action is still in progress right now.

In English, we usually say:

I have been trying...

That uses the present perfect continuous.
But in Spanish, with hace... que, the normal tense is often just the present:

• Hace veinte minutos que intento...
• literally: For twenty minutes now, I try / I am trying...
• natural meaning: I’ve been trying for twenty minutes

So even though the action started in the past, Spanish uses the present here because it is still ongoing.

In this structure, que is part of the expression hace + time + que + verb. It does not translate neatly as a separate English word.

You do not need to think of it as normal that. It is just the connector that links the time expression to the action.

So:

• Hace veinte minutos que estudio
• Hace dos años que vivo aquí
• Hace mucho tiempo que no lo veo

This whole pattern means have been doing something for...

Yes, absolutely. That is a very common alternative.

Both are natural:

• Hace veinte minutos que intento descifrar el acertijo
• Llevo veinte minutos intentando descifrar el acertijo

They both mean roughly the same thing: I’ve been trying to figure out the riddle for twenty minutes.

A small nuance:

• hace... que + present focuses on how long it has been happening
• llevar + time + gerund often feels a bit more focused on the accumulated duration of an ongoing action

In everyday speech, both are very common.

Yes, but the sentence structure changes a little.

You can say:

• Intento descifrar el acertijo desde hace veinte minutos

This also means I’ve been trying to figure out the riddle for twenty minutes.

So these are both correct:

• Hace veinte minutos que intento descifrar el acertijo
• Intento descifrar el acertijo desde hace veinte minutos

They are just two different Spanish ways to express the same idea.

Because that would not express the same idea naturally in Spanish.

If you want to say the action has been continuing for twenty minutes and is still happening, Spanish usually prefers:

• Hace veinte minutos que intento...
• Llevo veinte minutos intentando...
• Intento... desde hace veinte minutos

Using he intentado sounds more like you are talking about one or more attempts in the recent past, not one ongoing action over a duration.

Also, in standard Spanish, hace veinte minutos with a perfect tense often clashes with the intended meaning. It can sound unnatural if you mean for twenty minutes.

Yes, you can:

• Hace veinte minutos que estoy intentando descifrar el acertijo

This is grammatical and natural.

Difference in nuance:

• intento = a simple, neutral statement of the ongoing action
• estoy intentando = puts a bit more emphasis on the action being in progress right now

In many situations, both are fine. The version with intento is very common and elegant in this kind of time-duration structure.

Both can work, but they are not exactly identical.

• descifrar = to decipher, to crack, to figure out
• resolver = to solve

With acertijo (riddle), both are possible:

• descifrar el acertijo
• resolver el acertijo

Descifrar can suggest that the riddle feels like a code or something tricky to decode.
Resolver is a bit broader and more neutral: simply solve the riddle.

Because Spanish often uses the definite article when referring to a specific thing already understood in context.

So el acertijo means the riddle.

Without the article, descifrar acertijo would be ungrammatical here. You would normally need:

• descifrar el acertijo = figure out the riddle
• descifrar un acertijo = figure out a riddle

The article is required because acertijo is a countable noun and needs a determiner in this sentence.

Because por is usually not how Spanish expresses the duration of an action that has been continuing up to the present.

English says:

for twenty minutes

But Spanish usually does not translate that literally with por in this kind of sentence.

Instead, Spanish prefers:

• Hace veinte minutos que...
• Desde hace veinte minutos...
• Llevo veinte minutos...

Using por veinte minutos would usually suggest something different, such as a planned duration or a limited period in another context, not the standard have been doing for... structure.

Yes, it often does — but not in this sentence.

Compare:

• Empecé hace veinte minutos = I started twenty minutes ago
• Hace veinte minutos que intento descifrar el acertijo = I’ve been trying to figure out the riddle for twenty minutes

So the meaning depends on the structure:

• hace + time by itself often means ... ago
• hace + time + que + present verb means for ... now / have been ... for ...

That is a very important distinction.

Because Spanish usually leaves subject pronouns out when they are not needed.

The ending -o in intento already tells you the subject is I.

So:

• (Yo) intento descifrar el acertijo

Both are possible, but yo is normally omitted unless you want emphasis or contrast, for example:

• Yo intento descifrarlo, pero él ni siquiera quiere leerlo

In the original sentence, leaving out yo sounds more natural.

It is standard and natural across the Spanish-speaking world, including Spain.

A speaker from Spain would definitely say this, and so would many speakers in Latin America. The alternatives with llevar or desde hace are also widely used everywhere.

So this is not a Spain-only structure; it is general Spanish.