Do miradouro, vemos o vale.

Do is a contraction of de + o.

• de = a very common preposition that can mean from, of, about, and other things depending on context
• o = the (masculine singular)

So do miradouro literally contains the: from/of the viewpoint.

In this sentence, the natural sense is from the viewpoint / from the lookout point.

The article is already there inside do.

• do = de + o
• so do miradouro = from the viewpoint

This is very common in Portuguese:

• do carro = from the car / of the car
• da casa = from the house / of the house
• dos amigos = from the friends / of the friends

So you do not say de o miradouro in normal Portuguese; it contracts to do miradouro.

Because Do miradouro has been placed at the beginning of the sentence as a setting or viewpoint phrase.

The comma helps separate that introductory phrase from the main clause:

• Do miradouro, vemos o vale.

A more neutral word order would be:

• Vemos o vale do miradouro.

In short:

• Do miradouro, ... = fronted for style, focus, or rhythm
• the comma marks that pause

In everyday writing, the comma may sometimes be omitted, especially in short sentences, but with an introductory phrase like this, it is very natural.

Because Portuguese often drops subject pronouns when the verb ending already makes the subject clear.

• vemos = we see

The ending -mos tells you the subject is we. So nós is unnecessary unless you want emphasis or contrast.

Compare:

• Vemos o vale. = We see the valley.
• Nós vemos o vale. = We see the valley.
  This sounds more emphatic, like we see it.

This is very normal in European Portuguese.

Vemos is the 1st person plural present indicative of ver (to see).

The present tense of ver is:

• eu vejo = I see
• tu vês = you see
• ele/ela vê = he/she sees
• nós vemos = we see
• vós vedes = you see (plural, old-fashioned/rare in everyday speech)
• eles/elas veem = they see

So in this sentence, vemos means we see.

Depending on context, the Portuguese present can mean:

• something happening now: we can see
• a general fact or usual situation: we see

Because Portuguese usually uses the definite article with a specific, identifiable thing.

Here, o vale means the valley — a particular valley that the speakers can see from that place.

Without the article, vale would sound incomplete or unnatural in this sentence.

Compare:

• Vemos o vale. = We see the valley.
• Vemos vales. = We see valleys.
• Isto é um vale. = This is a valley.

So o is needed because the sentence is talking about a specific valley.

Yes. That is a very natural alternative.

• Do miradouro, vemos o vale.
• Vemos o vale do miradouro.

Both are correct. The difference is mainly one of word order and focus.

• Do miradouro, vemos o vale.
  starts with the location/viewpoint, so it gives that information more prominence
• Vemos o vale do miradouro.
  is a more straightforward, neutral order

English learners should notice that Portuguese is often flexible with this kind of phrase placement.

In this sentence, it most naturally means from the viewpoint, in the sense of from that place / from that vantage point.

Portuguese de can sometimes cover meanings that English expresses in different ways. Here the idea is:

• that is the place where you are standing
• and from there you can see the valley

So English may translate it as:

• From the viewpoint, we can see the valley
• or even more naturally, depending on context, At the viewpoint, we can see the valley

But grammatically, Portuguese uses de + o = do.

Yes, but the meaning or tone changes a little.

• Do miradouro, vemos o vale.
  the most natural simple version here
• Desde o miradouro, vemos o vale.
  possible, but less idiomatic in this situation; desde often emphasizes a starting point in space or time
• A partir do miradouro, vemos o vale.
  possible, a bit more formal or explicit: from the viewpoint / starting from the viewpoint

For an ordinary sentence about what can be seen from a location, do miradouro is a very natural choice.

Yes. In European Portuguese, miradouro is a very common word for a viewpoint, lookout point, or scenic overlook.

It is especially common in Portugal for places where people go to admire the view.

It is a masculine noun:

• o miradouro
• do miradouro
• um miradouro bonito = a beautiful viewpoint

So this sentence sounds very natural in a Portugal Portuguese context.