Learn Hardcore Finnish: Näkymä ikkunasta talvella on kaunis. - The view from the window is beautiful in winter.

The elative case (-sta/–stä) indicates movement or origin out of something. Here ikkunasta means “from the window.” You’re describing the view as seen from inside the window, so you need the elative.

Why is talvella in the adessive case (-lla) to express “in winter”?

In Finnish, seasons and many time expressions use the adessive case (-lla/–llä) to mean “during” or “in.” So talvella literally means “on/at winter,” which we translate as “in winter.”

Why does the adjective kaunis appear uninflected instead of matching näkymä in case?

When an adjective follows the verb olla (to be) as a predicative (e.g. “is beautiful”), it stays in the nominative singular form. Since näkymä is nominative singular, kaunis also remains in its basic nominative singular.

What form of olla is on, and why is it used here?

On is the 3rd person singular present tense of olla (to be). It corresponds to English “is,” linking the subject näkymä to the adjective kaunis.

How flexible is the word order in this sentence, and why is it arranged as it is?

Finnish has a flexible word order. The neutral sequence often places the subject first (näkymä), then adverbials (ikkunasta talvella), the verb (on), and finally the predicate (kaunis). You can move these elements around for emphasis without changing the core meaning.

How would you say “the view from my window in winter is beautiful”?

Attach the possessive suffix -ni to ikkuna before the case ending:
Näkymä ikkunastani talvella on kaunis.
Here ikkunastani means “from my window.”

Could you use talvessa (inessive) instead of talvella (adessive) for “in winter”?

No. Time expressions for seasons use the adessive (-lla/–llä), not the inessive (-ssa/–ssä). Therefore talvella is the correct form for “in winter.”