O percurso ora passa pelo ribeiro, ora sobe até ao cume.

It shows alternation. In this sentence, ora passa pelo ribeiro, ora sobe até ao cume means something like:

• at one point it goes by the stream, at another it climbs to the summit
• sometimes it passes by the stream, sometimes it climbs up to the summit

So it is not a one-time choice. It describes how the route alternates from one kind of section to another.

Not really.

Either ... or usually presents a choice between two possibilities.
Ora ... ora usually presents an alternation or changing situation.

So here the route is not choosing one of two options. Instead, the route sometimes does one thing, sometimes another as it continues.

It is perfectly correct, but it sounds a bit more written, descriptive, or literary than very casual speech.

In everyday conversation, people might also say things like:

• às vezes ... outras vezes ...
• por vezes ... por vezes ...

But ora ... ora is very natural in descriptions of landscapes, routes, narratives, and more polished writing.

Percurso means route, course, path, or itinerary, depending on context.

In this sentence, it refers to the route itself—for example a walking trail, hiking route, or marked path. It does not mean the act of walking it. So o percurso is the thing that passes by the stream and climbs to the summit.

They are in the present indicative, third person singular, because the subject is o percurso.

This kind of present tense is very common in descriptions:

• of routes
• of maps
• of landscapes
• in guidebooks

It is a descriptive present. English often does the same:

• The path goes along the river and then climbs to the top.

So it does not have to mean the route is doing this right now at this exact moment. It is just describing its general shape.

Pelo is the contraction of por + o.

• por + o = pelo

The verb here is passar por, which often means to pass by, to go through, or to pass along, depending on context.

So:

• passa pelo ribeiro = passes by / along / near the stream

The exact English wording depends on the situation, but grammatically the key point is that pelo comes from por + o.

By itself, it is a bit flexible. It most naturally suggests that the route passes by, along, or through the area of the stream.

It does not automatically mean the route literally crosses the water. If the sentence wanted to make a crossing clearer, Portuguese might use another wording, depending on the context.

So in a route description, passa pelo ribeiro usually suggests that the path runs near the stream or through the stream area.

Ribeiro usually means a small stream, brook, or creek.
Rio means river.

So ribeiro is generally smaller than rio. In a landscape description, choosing ribeiro helps create a more precise image: this is not a big river, but a smaller watercourse.

Ao is the contraction of a + o.

• a + o = ao

So até ao cume means up to the summit or as far as the summit.

In European Portuguese, this kind of contraction is very normal and natural. So:

• até ao cume = until/up to the summit

The important thing for a learner is simply to recognise ao as a + o.

Cume means summit, peak, or top, especially of a mountain or hill.

It is more specific than topo:

• cume = the summit/peak of a mountain or high point
• topo = the top of something more generally

So in a hiking or landscape context, cume is the more precise word.

The commas separate the two balanced parts of the ora ... ora structure:

• ora passa pelo ribeiro
• ora sobe até ao cume

This punctuation helps show the rhythm of alternation and makes the sentence easier to read. It is a very natural way to punctuate this kind of structure.