Ora subimos a encosta, ora descemos até ao vale.

Here ora ... ora ... is a correlative expression that means something like:

• now ... now ...
• at one moment ... at another ...
• sometimes ... sometimes ...

So Ora subimos a encosta, ora descemos até ao vale shows an alternation: first one thing happens, then the opposite happens.

It is a fairly literary or descriptive way to present changing movement or changing situations. In more everyday English, the idea is:

• At times we go up the slope, at times we go down into the valley.

It does not mean the time word ora in the sense of now on its own. In this structure, it works as part of a pair: ora X, ora Y.

Portuguese often uses the present tense to describe:

• habitual actions
• repeated actions
• a scene being vividly narrated

So subimos and descemos can mean:

• we go up / we go down
• we are going up / we are going down, in a descriptive narrative sense
• we keep going up / we keep going down, depending on context

In this sentence, the present tense helps create the image of an ongoing route or repeated movement: sometimes the path rises, sometimes it falls.

Also, subimos and descemos are forms for we.

It can mean both, depending on context.

• subir = to go up, to ascend, to climb
• descer = to go down, to descend

In subimos a encosta, the idea is not necessarily that you are climbing with your hands like climbing a wall. It is more naturally we go up the slope or we climb the slope.

So subir is broader than English to climb. It often simply means movement upward.

Because here a encosta is the direct object of subir in the sense to go up the slope.

So:

• subir a encosta = to go up the slope
• subir a montanha = to go up the mountain
• subir as escadas = to go up the stairs

There is no preposition a here, so there is no contraction.

That is why it is:

• subimos a encosta

and not:

• subimos à encosta

If you said à encosta, that would suggest the preposition a plus the article a, which would be a different structure.

Because ao is the contraction of:

• a + o = ao

Here the noun vale is masculine singular, and it appears with the definite article o:

• o vale = the valley

After até, European Portuguese very commonly uses the article when the noun normally takes one:

• até ao vale
• até à praia
• até aos montes

So até ao vale means as far as the valley or down to the valley.

This is a very common learner question, and the answer is that the two nouns are in different grammatical structures.

In subimos a encosta:

• a encosta is not preposition + article
• it is simply the slope as the direct object

In até ao vale:

• ao is a + o
• this really is a preposition followed by the article

So the difference is not mainly about one noun needing an article and the other not needing one. It is about the role each noun plays in the sentence.

You could think of it like this:

• subir a encosta = go up the slope
• descer até ao vale = go down to the valley

Yes, this wording is especially typical of European Portuguese.

In European Portuguese, using the article after até is very common:

• até ao vale
• até à cidade
• até aos campos

In Brazilian Portuguese, you may also hear forms without the article more often, depending on style and region:

• até o vale
• sometimes even just até vale in certain contexts, though that is less standard here

For a learner focusing on Portugal, até ao vale is perfectly natural and very useful to learn.

• encosta = slope, hillside, side of a hill or mountain
• vale = valley

So the image is of a route through uneven terrain:

• sometimes we go up the slope
• sometimes we go down into the valley

Encosta is not just any hill. It refers more specifically to the sloping side of higher ground.

The comma separates the two matching parts of the ora ... ora ... structure:

• Ora subimos a encosta, ora descemos até ao vale.

This punctuation makes the alternation clearer and gives the sentence a balanced rhythm.

It is similar to how English might punctuate:

• Now we go up the slope, now we go down into the valley.

So the comma is very natural here.

Yes. Ora ... ora ... is correct and elegant, but there are more neutral alternatives.

For example:

• Às vezes subimos a encosta, às vezes descemos até ao vale.
• Umas vezes subimos a encosta, outras vezes descemos até ao vale.
• Por vezes subimos a encosta, por vezes descemos até ao vale.

These all keep the same general idea of alternating movement, but ora ... ora ... sounds a bit more literary or descriptive.

A simple learner-friendly approximation would be:

• Ó-ra su-BI-mush a en-KOSH-ta, ó-ra de-SSE-mush a-TÉ aw VA-le.

A few useful pronunciation notes:

• subimos and descemos in European Portuguese often sound like they end in something close to -mush
• encosta has the stress on -cos-
• até has stress on the final syllable
• ao sounds roughly like ow
• vale has two syllables: VA-le

If you want, the rhythm is quite balanced:

• Ora subimos a encosta, / ora descemos até ao vale.

Yes. It is a general pattern, not something limited to movement verbs.

For example:

• Ora chove, ora faz sol.
  Sometimes it rains, sometimes it is sunny.

• Ora ri, ora chora.
  Now she laughs, now she cries.

• Ora concorda, ora discorda.
  At times he agrees, at times he disagrees.

So in your sentence, it is simply being used to show alternating actions: going up and going down.