Quite honestly, once you're in Denver, it's easier to rent/borrow
a car than fly anyplace within an hour. It's an hour's drive
to Colorado Springs, which means you can drive and visit the
USAF academy, drive to the Garden of the Gods, drive to Culver's
for custard, etc. From APA it's less than an hour's drive to
Boulder (traffic permitting). There are some trips that really
don't make sense flying.

On the other hand....2.5 hours to Sante Fe flying. 1 hour
flying to Pueblo and there's a little museum there, and you
can usually borrow the field car to drive into Pueblo.