Learn Hardcore Finnish: Minä matkustan Lappiin junalla.

Lappiin is in the illative case, which indicates movement into something (“into Lapland”). For many Finnish nouns the illative singular is formed with -in or -iin, so Lappi → Lappiin.

What case is junalla, and why does it mean “by train”?

junalla is in the adessive case (suffix -lla/-llä). In Finnish the adessive often expresses the means or instrument of an action, so junalla literally means “on/with a train” → “by train.”

Why is the pronoun Minä included? Must I always say it?

Subject pronouns in Finnish are optional because the verb ending already shows the person. You include Minä mainly for emphasis or clarity. Otherwise you can simply say Matkustan Lappiin junalla.

What is the infinitive of matkustan, and how is the verb conjugated?

The infinitive is matkustaa (“to travel”). For the 1st person singular present you drop -aa and add -an, giving matkustaa → matkustan (“I travel”).

Can I change the word order in this sentence?

Yes. Finnish has fairly free word order. For example:
• Junalla matkustan Lappiin (By train, I travel to Lapland.)
• Lappiin matkustan junalla (To Lapland, I travel by train.)
Each variation shifts the focus slightly.

Why is the consonant p doubled in Lappiin?

This is consonant gradation. The strong grade of Lappi’s root is pp. In the illative singular the strong grade remains, so you get pp + iin = Lappiin.