Get coffee at Macy's, Rendezvous, or Late for the Train, enjoy a beer at one of the many microbreweries, eat some fantastic food, listen to music (either on a corner or in an establishment), or join in whatever festivities are happening in Heritage Square.
This place is rad. Pluto was discovered here and that's just the beginning of how amazing this place is. There is a new observation deck that just opened in the summer of 2019, and that's in addition to the telescope, workshops, talks, and awesome exhibits they already had at the facility. Go explore space up close and personal.
Take a little time out of your day to walk a loop at the park. It's a great place to see what Flagstaff is really about. You'll often see deer hanging out while people take their dogs for a walk or a run. You'll get great views of the San Francisco Peaks, Mount Elden, and it's also a great place to get some mellow exercise while in nature.