Learn Hardcore French: Le parc auquel nous allons est magnifique.

It refers back to le parc (the park).
It is required because the verb aller is used with the preposition à (aller à un parc = to go to a park).
So auquel nous allons literally means “to which we are going”.

Structurally, the sentence is:

Le parc – auquel nous allons – est magnifique
The park – to which we are going – is magnificent

Why can’t we just say Le parc que nous allons est magnifique?

Because que is the relative pronoun used for direct objects, and here the park is not a direct object of aller.

Que = “that/which” when it is the direct object of the verb in the relative clause.
- e.g. Le livre que je lis = The book that I’m reading (I’m reading the book → book = direct object).
But aller does not take a direct object. You say:
- aller à un parc (go to a park), not aller un parc.

So in the relative clause, the park is linked to aller via the preposition à, so you need a form that includes à:

Le parc auquel nous allons ✅
Le parc que nous allons ❌ (ungrammatical)

What is auquel made of, grammatically speaking?

Auquel is a combination of the preposition à and the relative pronoun lequel:

à + lequel → auquel (masculine singular)

Other important forms:

à + lequel → auquel (masc. sing.)
à + lesquels → auxquels (masc. plural)
à + lesquelles → auxquelles (fem. plural)
à + laquelle → à laquelle (fem. sing., no contraction)

Similarly with de:

de + lequel → duquel
de + lesquels → desquels
de + lesquelles → desquelles
de + laquelle → de laquelle

In the sentence, parc is masculine singular (le parc), so you use auquel.

Could we replace auquel with où and say Le parc où nous allons est magnifique?

Yes, that’s perfectly correct and, in fact, more common in everyday speech:

Le parc auquel nous allons est magnifique. (more formal / written)
Le parc où nous allons est magnifique. (very natural, common)

Où can replace à lequel, dans lequel, etc. when you’re talking about a place:

La ville où j’habite. = The city where I live.
(literally la ville dans laquelle j’habite)

So here, because parc is a place, où works very well.

So when should I use auquel and when should I use où?

General guideline:

For places (or times):
- Où is common and often simpler:
  - Le parc où nous allons.
  - Le jour où je suis arrivé.
- Auquel is more formal and precise, and is used if you want to keep the specific preposition à:
  - Le parc auquel nous allons (emphasizes to which).
For things that are not places:
- Use auquel (not où) when the verb requires à:
  - Le problème auquel je pense = The problem that I’m thinking about
    (penser à quelque chose)

Here, both are correct, but Le parc où nous allons… is what you’d hear most often in conversation.

Why is it auquel and not à lequel here?

Because in standard French à + le always contracts to au:

à + le → au
à + lequel → auquel

You don’t say à le parc, you say au parc.
Similarly, for the relative pronoun you don’t say à lequel parc nous allons but auquel nous allons.

In practice:

Le parc auquel nous allons ✅ (normal, standard)
Le parc à lequel nous allons ❌ (sounds wrong to native speakers)

Why does auquel have to match le parc in gender and number?

Relative pronouns like lequel agree in gender and number with the noun they refer to (their antecedent).

Antecedent: le parc → masculine, singular.
Therefore, you must use the masculine singular form: lequel → auquel when combined with à.

If the noun were different, the form would change:

La ville à laquelle nous allons… (fem. sing.)
Les parcs auxquels nous allons… (masc. plur.)
Les villes auxquelles nous allons… (fem. plur.)

What is the role of auquel nous allons in the sentence structure?

Auquel nous allons is a relative clause that modifies le parc.

Breakdown:

Le parc → the noun being described (subject of the main verb est).
auquel nous allons → relative clause specifying which park.
est magnifique → main clause (verb + adjective).

So the core is:

Le parc … est magnifique.
The relative clause inserted in the middle gives extra information about which park: the one we’re going to.

Is there any difference if I add commas: Le parc, auquel nous allons, est magnifique?

Yes, it slightly changes the nuance, just like in English.

Without commas:
Le parc auquel nous allons est magnifique.
→ “The park that we are going to is magnificent.”
This tends to sound like you’re specifying which park (out of several).
With commas:
Le parc, auquel nous allons, est magnifique.
→ “The park, which we are going to, is magnificent.”
Here the clause is extra information, as if there is only one relevant park and you’re just adding a side comment.

Grammatically both are correct; the version without commas is more common in simple examples like this.

How do you pronounce auquel, especially in Le parc auquel…?

Pronunciation:

auquel → /okɛl/ (roughly: oh-kell).

In the full phrase Le parc auquel nous allons:

parc → /paʁk/
There is usually a liaison: parc_auquel → /paʁk‿okɛl/
(you hear the k carry over: par-koh-kell).

So you’d pronounce:

Le parc auquel nous allons est magnifique →
/lə paʁk‿okɛl nu.z‿alɔ̃ ɛ maɲifik/