Bonjour Sayli,

The noun "endroit" is used here in the plural -- endroits, but the adjective magnifique is after the noun.

So what we have here is the indefinite article des being used in front of the plural noun therefore des endroits magnifiques.

https://www.lawlessfrench.com/grammar/de-vs-du-de-la-des/

Have a look at the above link  --  I think it will help you to understand more fully.

Hope this helps.

Bonne continuation.

Jim