Learn Finnish: Me kiipeämme maapallon korkeimpaan vuoristoon. - We are climbing to the globe's highest mountain range.

To make korkea (high) superlative, we need a superlative stem. Because the word is going into the illative case, we use the strong superlative stem -impa-, giving us korkeimpa-. To make it illative, we double the last vowel and add -n, resulting in korkeimpaan (into the highest).

Why do we use the illative case for korkeimpaan vuoristoon?

The verb kiivetä (to climb) requires the illative case when you are expressing the destination you are climbing to. In Finnish, you climb "into" a mountain range, so both the adjective and the noun take their illative endings (-aan and -oon).

Kiipeämme means "we climb", but the dictionary form is kiivetä. Why does the v change to a p?

Kiivetä is a Type 4 verb. These verbs have "reverse" consonant gradation: they are weak in their dictionary form but become strong when conjugated. Here, the weak v strengthens to a p. After modifying the stem, we add the personal ending -mme to get kiipeämme.

What is the suffix -sto doing in the word vuoristoon?