Learn Swedish: Vi vandrade på fjället igår. - We hiked on the mountain yesterday.

This is the simple past tense (preteritum) of the verb att vandra (to hike). Vandra is a regular Group 1 verb. For all Group 1 verbs, you create the past tense by adding -de to the base form, which always gives you that signature -ade ending.

Why use fjället for "the mountain" instead of berget?

Ett berg is the general Swedish word for a mountain. Ett fjäll is a specific type of mountain or highland found in Scandinavia that is high enough to go above the tree line (often called a "fell" in English). Hiking on fjället is a classic Swedish outdoor activity.

In English we usually say we hike "in" the mountains. Why does this sentence use på (on)?

In Swedish, you focus on the fact that you are walking on the open surface of the terrain, so you use på (on). If you said you were hiking i fjället, it would sound like you were walking in a cave inside the mountain!

If I want to start the sentence with Igår (yesterday), how does the word order change?