Learn Finnish: Otimme valokuvan museossa. - We took a photograph in the museum.

Otimme is the past tense of the Type 1 verb ottaa (to take). First, the strong tt weakens to a single t. Then, we apply the past tense vowel mutation: while many Type 1 verbs change their final a to o, verbs that already have an o or u in the first syllable change their final a to i (the a drops out leaving just the past tense marker i). So, the stem otta- becomes oti-, and we add -mme for "we".

Why does valokuvan end in -n?

It is the object of the sentence. Because we took a whole photograph and the action is complete, the object takes the -n ending to show a total, finished action. This form is often called the genitive-accusative.

Is valokuva a compound word?

Yes! It is made by combining valo (light) and kuva (picture or image). So a photograph is literally a "light picture" in Finnish.

Why is it museossa and not museon?