Learn French: Vous allez à Tahiti afin de voir ce paysage pittoresque. - You are going to Tahiti in order to see this picturesque landscape.

In French, most single islands that don't have a definite article in their name (like Tahiti, Cuba, or Madagascar) take the preposition à for "to" or "in". If an island region has a feminine or masculine article (like la Corse or le Japon), it usually takes en or au.

If I wanted to say "I am returning from Tahiti", which preposition would I use?

You would use de. Just as single islands without articles take à for "to" or "at", they take de (or d' before a vowel) for "from". So, "I am returning from Tahiti" is Je rentre de Tahiti.

What is the difference between using afin de and just using pour here?

Both afin de and pour mean "in order to" and must be followed by an infinitive verb (like voir). However, afin de belongs to a slightly more formal register. Using it is a great way to elevate your written French or sound more polished when speaking.

Why doesn't the adjective pittoresque change form here?

The noun paysage is masculine, but because the adjective pittoresque already ends in an -e in its base form, it does not change spelling for feminine nouns either. It would only change to add an -s if the noun were plural.