If you don’t have time or wish to go far away from the city, Helsinki Central Park can be a good option for longer walks.
Here you can find the usual wide park roads, nature paths, different birds, edible berries, and a river.
The landscape is pretty typical for Helsinki: a lot of rocks, mixed forest, etc.
There are several hiking routes in the park, which you can easily find on the MyHelsinki webpage or the AllTrails application.
Remember that this huge park is still in the city center, so cars and other noises can be easily heard. Besides that, the place is popular and usually full of other people and cyclists.
There is a pet cemetery in the park, a very dreadful sight, would recommend that to cold-hearted people only.