A trip to Colorado is always great to start with a few days in Denver, the mile high city. This way you can acclimate to the higher altitude and check out some awesome things in the area.
16th Street Mall
Denver Botanic Gardens
Red Rocks Amphitheater
Rino Graffiti tour (start at Market & 28th and walk North)
Arriving at Denver International Airport, the Denver Light Rail runs from the Airport directly to Denver Union Station.
There are hotels at Denver Union Station or take the light rail further or an Uber to pick up a rental car
Downtown Denver also has plenty of Lime Scooters typically
There are lots of nice hotels in downtown Denver, close to Union Station to limit renting a car the first day or so.