Eagle County Regional Airport (Vail/Eagle): The best airport for a rental-car trip: drive west on I-70 to Glenwood Springs in roughly 35–45 minutes, weather permitting. There is no frequent, simple airport-to-Glenwood transit transfer worth choosing over a prebooked shuttle or rental car; rideshare availability can be thin.
Aspen/Pitkin County Airport: About 45–60 minutes by car in clear conditions, but this is not the easy option: winter weather and Roaring Fork Valley traffic can make it slower. A rental car is simplest; RFTA buses can connect Aspen and Glenwood but are better for travelers already staying in the valley than for hauling airport luggage.
Grand Junction Regional Airport: Rent a car and take I-70 east; allow about 80–90 minutes to downtown Glenwood Springs. This is a sensible western-arrival option, especially if you are continuing toward Palisade or Utah, but there is no particularly useful airport public-transport transfer.
Denver International Airport: Do not rent a car solely to endure the mountain drive if Glenwood is your only stop. Take the A Line to Denver Union Station, then Amtrak’s daily California Zephyr to Glenwood Springs (about 5½ hours from Denver; book early). Bustang also links Denver with Glenwood Springs, but schedules are less elegant than the train and should be checked carefully.
Glenwood Springs Amtrak Station: The California Zephyr stops at 7th Street in the center of town, walking distance to the Hot Springs, downtown hotels, restaurants, and the river. It is the unusually good arrival: the Denver–Glenwood segment runs through Glenwood Canyon in daylight and reaches places the road does not.