Depends on which way you go. The fastest way is I-70 to US 40 thru Granby, then Co 125 up to Walden. Trip takes about 2 and a half hours from Denver.
You can also take highway 14 from Fort Collins, but coming from Denver it will add an hour to your drive time
You can also take highway 14 from Fort Collins, but coming from Denver it will add an hour to your drive time