Learn Finnish: Kävelin puiston läpi. - I walked through the park.

While you are currently learning about postpositions that require the partitive case (like kohti or varten), läpi is a common postposition that requires the genitive case (puiston). It is likely included here to help you practice telling them apart and to remind you that the genitive is the default case for most postpositions.

Could I put läpi before the noun and say läpi puiston?

Yes, läpi is one of the flexible words that can act as either a postposition (after the noun) or a preposition (before the noun). Both puiston läpi and läpi puiston are correct and use the genitive case, though placing it after the noun is much more common in everyday Finnish.

How does läpi differ from kautta, which can also mean 'through'?

Läpi gives a stronger physical sense of piercing or going inside and out the other side of a space, like walking through a park, a door, or a dense forest. Kautta translates closer to 'via' or 'by way of' and is used for routes, like traveling through a town on your way to another city.

What is the rule for forming the past tense kävelin from kävellä?