El sender arriba al refugi.

Because a + el contracts to al in Catalan.

So:

• a + el refugi → al refugi

This is very common and works much like contractions in other Romance languages.

Examples:

• Va al poble. = He/She goes to the village.
• Arriba al cim. = It reaches the summit.

A useful contrast:

• a la casa stays a la casa
• a l’estació stays a l’estació

Only a + el becomes al.

Arriba is the 3rd person singular present tense of arribar.

In this sentence, it agrees with el sender, which is singular:

• el sender = the path
• arriba = arrives / reaches

With things like paths, roads, trails, or stairs, Catalan often uses arribar a in a way that English may express as reach, lead to, or sometimes go to.

So here arriba al refugi means the path reaches or leads up to the refuge/shelter.

Yes. In Catalan, it is normal to use arribar a with inanimate things such as:

• un camí
• un sender
• una carretera
• unes escales

This means that the path/road/stairs reach a place.

Examples:

• La carretera arriba al poble.
• Aquest camí arriba al riu.

In English, the path arrives at the refuge sounds less natural, so English usually says:

• The path reaches the refuge
• The path leads to the refuge

But in Catalan, arribar is perfectly natural here.

Sender is a masculine noun meaning path, trail, or footpath.

It takes the masculine singular article:

• el sender

Plural:

• els senders

A very common alternative in Catalan is camí, which is also masculine:

• el camí

Very roughly:

• sender often suggests a narrower trail or footpath
• camí can be more general

So El sender arriba al refugi is completely natural if you are talking about a trail in the countryside or mountains.

Catalan often uses definite articles where English also uses the:

• el sender = the path
• el refugi → after contraction, al refugi = to the refuge / at the refuge

The noun refugi is masculine singular, so it takes el:

• el refugi
• al refugi

If it were feminine, you would use:

• la
• a la

For example:

• La ruta arriba a la cabana.

It can mean more than one thing depending on context.

Refugi can mean:

• a refuge
• a shelter
• very often in mountain contexts, a mountain refuge/hut

So if the sentence is about hiking, refugi will often refer to a mountain shelter or hut rather than the abstract English word refuge.

That is why context matters a lot with this word.

Because the subject is singular:

• El sender = singular
• so the verb must also be singular: arriba

Compare:

• El sender arriba al refugi. = singular
• Els senders arriben al refugi. = plural

This is basic subject-verb agreement.

A quick present tense mini-pattern for arribar:

• jo arribo
• tu arribes
• ell/ella arriba
• nosaltres arribem
• vosaltres arribeu
• ells/elles arriben

Very often, yes, when you say where someone or something arrives/reaches.

Examples:

• Arribo a casa.
• Arriben al poble.
• El camí arriba al llac.

So in your sentence:

• arriba al refugi the a is part of the normal pattern.

This is one reason English speakers need to be careful: Catalan often uses arribar a + place, while English may use arrive at/in or simply reach.

Yes, but El sender arriba al refugi is the most neutral and straightforward order.

Catalan usually prefers:

• Subject + Verb + Complement

So:

• El sender
  • arriba
    • al refugi

Other orders are possible for emphasis or style, but they are less basic for a learner.

For example:

• Al refugi arriba el sender would sound marked or literary in most contexts.

So the original order is the one you should learn first.

A simple pronunciation guide is:

el sen-DER a-RRI-ba al re-FU-gi

A few notes:

• rr in arriba is a rolled or trilled r
• the stress is on -der in sender
• the stress is on -ri- in arriba
• the stress is on -fu- in refugi

A rough IPA pronunciation in standard Central Catalan is: [əl sənˈde arˈriβə əl rəˈfuʒi]

If you are a beginner, the most useful thing is to notice the stress pattern and the rolled rr in arriba.