Great Sand Dunes
Trip Date: January
Location: Great Sand Dunes National Park
Miles: 2-10, depending on how far into the dunes you want to explore
Start/Finish: Medano Creek Parking or Point of No Return
Permit Required?: Yes. No quota. Available for free at the Visitor Center
Season: Year Round; every time I have backpacked into the Dunes has been in the dead of winter (January). Temperatures were cold (around 0 degrees at night on one occasion) but you'll have the place to yourself. Be sure to check the forecast diligently for a time frame where the wind is predicted to be 5 mph or less.
Directions: Found here