Learn Finnish: Matkustan Viroon lautalla. - I travel to Estonia by ferry.

In Finnish, the adessive case ending -lla or -llä is used to express the instrument or means you use to do something. For transportation, it does the job of the English word "by". Since lautta is "ferry", lautalla means "by ferry".

The dictionary word for ferry is lautta. Why is there only one 't' in lautalla?

This happens because of consonant gradation. Adding the -lla ending closes the final syllable. When a syllable is closed by an ending, a strong consonant combination like 'tt' weakens into a single 't'. Therefore, lautta becomes lautalla.

Why is the destination Viro (Estonia) written as Viroon here?

Because you are traveling to a destination, you need the illative case (the "into" case). For words ending in a short vowel like Viro, you form this case by doubling the final vowel and adding -n. So, Viro becomes Viroon.

Could I change the word order and say Matkustan lautalla Viroon?

Yes, absolutely! Finnish word order is quite flexible. The sentence's current order (Matkustan Viroon lautalla) sounds very natural and places a slight emphasis on the fact that you are taking the ferry. Putting lautalla before the destination is also perfectly correct.