Learn French: Ce détour, nous allons le prendre pour éviter la ville. - This detour, we are going to take it to avoid the city.

This is a structure called left dislocation. To emphasize the topic of the sentence (Ce détour), French speakers often pull it to the front. When you do this, you must add a clitic pronoun (le) later in the sentence to double that fronted noun. A standard, non-emphasized version would just be: Nous allons prendre ce détour...

Why is the pronoun le placed before prendre rather than before allons?

When a sentence has a conjugated verb followed by an infinitive (like the near future allons prendre), object pronouns almost always go directly in front of the infinitive they belong to. Because the action happening to the detour is the taking (prendre), the pronoun le sticks to prendre.

How would this sentence look if we used right dislocation instead?

Right dislocation moves the emphasized topic to the end of the clause, often as a sort of clarification. It would look like this: Nous allons le prendre, ce détour, pour éviter la ville. The pronoun le remains exactly where it is!

Why do we need pour before éviter? Doesn't the infinitive already mean 'to avoid'?

In English, 'to avoid' expresses both the action and the purpose ('in order to avoid'). In French, the infinitive éviter just names the action. To express the idea of 'in order to' or 'for the purpose of', you must use the preposition pour before the infinitive.