Diumenge volem fer una excursió a la muntanya amb una motxilla petita.

In Catalan, days of the week often appear without a preposition when you mean on Sunday, on Monday, etc.

So:

• Diumenge = on Sunday
• Dilluns = on Monday

This is very normal in Catalan. English needs on, but Catalan usually does not.

A useful contrast:

• Diumenge anirem a la platja. = We’ll go to the beach on Sunday.
• Els diumenges anem a la platja. = We go to the beach on Sundays.

So the bare day name often refers to a specific day, while els + day often gives a habitual meaning.

Yes—days of the week are normally lowercase in Catalan:

• diumenge
• dilluns
• dimarts

It is capitalized here only because it is the first word of the sentence. If it appeared in the middle, it would usually be lowercase:

• Volem fer una excursió diumenge.

Volem is from the verb voler, which means to want.

Here it is the 1st person plural present tense:

• jo vull = I want
• tu vols = you want
• ell/ella vol = he/she wants
• nosaltres volem = we want
• vosaltres voleu = you all want
• ells/elles volen = they want

So volem means we want.

In this sentence, it expresses a present intention about the future, just like English often does:

• Volem fer una excursió diumenge. = We want to go on an excursion / hike on Sunday.

Catalan often uses fer very broadly, in places where English uses more specific verbs.

So:

• fer una excursió literally looks like to do/make an excursion
• but naturally it means to go on an excursion, to go on a trip, or sometimes to go on a hike, depending on context

This is a very common Catalan pattern. Compare:

• fer una passejada = to take a walk
• fer un viatge = to take a trip
• fer esport = to do sports / exercise

So even if fer looks very general, it is often the normal verb to use.

Excursió is a fairly broad word. It can mean:

• an excursion
• an outing
• a trip
• sometimes a hike, depending on where you are going

Because the sentence says a la muntanya (to the mountains / mountain area), an English translation like a hike may feel natural. But the Catalan word itself is not limited only to hiking. It suggests a leisure trip or outing, often outdoors.

Because muntanya is a feminine noun:

• la muntanya = the mountain

The preposition a combines with the article:

• a + la = a la
• a + el = al

So:

• a la muntanya = to the mountain / in the mountains
• al parc = to the park
• al poble = to the town

Since muntanya is feminine, a la is correct.

It can depend on context. Literally, a la muntanya is to the mountain or to the mountain area, but in natural English it is often better translated as:

• to the mountains
• into the mountains
• in the mountains

Catalan often uses the singular where English may prefer the plural or a more idiomatic phrasing. So you should not always translate word-for-word.

In this sentence, a la muntanya suggests going to a mountain/nature area for the excursion.

In Catalan, adjectives usually come after the noun.

So:

• una motxilla petita = a small backpack

This is the most neutral, normal order.

Catalan can sometimes place an adjective before the noun, but that is less common and often gives a more literary, emphatic, or subjective tone. For basic learning, the safest rule is:

• noun + adjective

Examples:

• una casa gran = a big house
• un cotxe nou = a new car
• una motxilla petita = a small backpack

Because Catalan articles and adjectives must agree with the noun in gender and number.

Here the noun is motxilla, which is:

• feminine
• singular

So the words around it must match:

• una = feminine singular indefinite article
• petita = feminine singular adjective

Compare:

• un llibre petit = a small book
• una motxilla petita = a small backpack
• unes motxilles petites = some small backpacks

This agreement is a core feature of Catalan grammar.

Amb means with.

In this sentence, amb una motxilla petita most naturally means that the people are going with/carrying a small backpack.

So it describes accompaniment or what they have with them.

Examples:

• Vaig amb la meva germana. = I’m going with my sister.
• Vaig amb una motxilla. = I’m going with a backpack / carrying a backpack.

In your sentence, amb una motxilla petita gives extra detail about the excursion.

In practice, it describes the situation of the action—that the excursion is done with a small backpack.

In English, we might think of it as modifying the whole event:

• We want to go on a mountain excursion with a small backpack.

It does not usually mean that the backpack itself is somehow accompanying the noun excursió in a strict grammatical sense. It is just an added phrase giving context about how or with what they are going.

Catalan word order is somewhat flexible, though the original version is very natural.

Original:

• Diumenge volem fer una excursió a la muntanya amb una motxilla petita.

Possible alternatives:

• Volem fer una excursió a la muntanya diumenge.
• Diumenge volem fer amb una motxilla petita una excursió a la muntanya.
  This is grammatical, but less natural.

Catalan usually prefers a fairly clear order:

• time
• verb
• object
• place
• extra details

So the original sentence sounds smooth and normal.

The accent mark in excursió shows where the stress falls: on the final syllable.

So it is pronounced roughly like:

• ex-cur-si-Ó

The written accent helps indicate the stressed syllable and also distinguishes it from what the default stress pattern would otherwise suggest.

Accent marks in Catalan are very important because they often tell you how a word is pronounced.

The important part is ny, which in Catalan is pronounced like the ny in canyon or the ñ in Spanish montaña.

So muntanya is roughly:

• mun-TA-nya

That ny sound is very common in Catalan:

• Catalunya
• any
• senyor does not have ny, so do not confuse it—but ny itself always has that palatal sound.

So muntanya is a good word to practice for that sound.