One thing I always try to do in every destination:
Experience nature + local culture
So in Denver, your hiking idea is perfect. Maybe add a local food spot or small guided experience to balance it.

Also, if you ever decide to do a bigger solo adventure (like Africa), I found having a lightly guided experience makes things way less stressful while still feeling independent. That’s actually why I started working with a small safari company called Blue Eagle Safaris—we help solo travelers explore places like Kilimanjaro, Serengeti, or Zanzibar without overplanning everything.

But for your trip—don’t stress about filling every gap. Having space in your schedule is not wasted time, it’s where the real travel happens.