Climb Lindenhof Hill. It’s actually less daunting than it sounds. The ‘hill’ is basically just an incline (with steps) you can walk up to get a nice view of the Limmat River.
Go hiking at Uetliberg. This is a park that’s about 20 minutes outside of Zürich and easily accessible by train. You can also go mountain biking, or do the solar system walk, which is a path built to scale of the solar system. Ben and I took a wrong turn but that worked out for the best. It led us to the Uetliberg observation tower, which we climbed to get a view of Zürich from 236 feet up in the air. It’s not for the faint of heart though. I’m not usually afraid of heights but still avoided looking down through the steps, and my legs felt a little wobbly.