@Jsan22 - I would definitely recommend heading to Red Rocks Park and Amphitheatre . Although it is most popular as an outdoor music venue, I love taking Denver visitors there during the day to hike around. May in Colorado can be hit or miss weather-wise, but Red Rocks is still a great place to visit even when it's cold and snowy.
Thanks for the follow up question!
Can you clarify for us what you mean by 'flying trips'? Are you asking about a 'flight seeing' trip in a plane or a helicopter or are you looking for a fly fishing company? There is so much to see in Colorado and great fly fishing too!