Knox Mountain Park is just north of downtown Kelowna. It has an extensive network of hiking and biking trails. There is a road accessible lookout usually open from mid March to mid November (frost-free months).
For hiking, I'd recommend Paul's Tomb for an easy walk. It is 4.8km return but you can just turn around whenever you prefer. This classic Kelowna trail curves around the base of Knox Mountain (slight downhill) to a pretty pebble beach backdropped by crystal clear water.
For a bigger challenge and pay-off, check out the Apex Trail. The well used trail switchbacks its way up the side of Knox Mountain, rewarding hikers with spectacular views of Kelowna and Okanagan Lake. It is 4.2km return with 260m elevation gain.