Breakdown of Milloin kävit viimeksi saunassa?
sauna
sauna
milloin
when
käydä
to visit, to go (and come back)
viimeksi
last time, most recently
Questions & Answers about Milloin kävit viimeksi saunassa?
Why do we use viimeksi here instead of just viime?
The word viime is an indeclinable modifier that must be attached directly to a time noun, like viime viikolla (last week). Because this sentence doesn't have a time noun, we use the adverb viimeksi (last / for the last time), which is formed with the translative case ending -ksi.
Why is the noun in the inessive case (saunassa) instead of the illative (saunaan), since the English translation is 'go to'?
If I want to answer this question using 'last week', how does the word viime behave?
You would say viime viikolla. The modifier viime is indeclinable, meaning it never changes its form or takes any case endings, even though the noun viikko takes the adessive ending -lla to indicate when something happened.
Is the word order strict here, or could I put viimeksi at the end of the sentence?
The word order is flexible, and putting viimeksi at the end is perfectly correct. Placing it right after the verb kävit just gives it a slight natural emphasis in the flow of the sentence.