Genesee Mountain is a nice hike that isn’t too hard and is easy to get to. The bonus is that there is a herd of bison that live nearby.
The Brainard Lake Recreation Area is one of my favorite places to hike in summer. I tried Brainard: Long Lake Loop (winter) and it was great.
The Ridgeline Open Space Loop in Castle Rock is a ten mile hike with plenty of hills for a great workout and some nice views as a reward.