We’re going to Estes Park/ RMNP for a week this summer. Flying in/out of Denver. I’ve got 4 additional nights (including July 4). Where should we go? Parents and 3 high school/ college kids.

Rental vehicle prices were a bit steep in Denver even before the pandemic. Some of the rental companies sold off some of their fleets so prices may be even higher this summer. I'm hoping that all of you will be vaccinated by then. If you want to stay east of the Rockies, you could go to Colorado Springs or down to Great Sand Dunes NP.

I've always enjoyed the loop from Grand Lake and then northward towards Walden then through Poudre Canyon and on to Fort Collins. There is a gravel road 'shortcut' from Rand over to 14 if you want to skip Walden. There are some cabins around Rustic, if you're inclined to spend a night. I believe, surprisingly, that the Poudre River has the only federal wild and scenic designation in Colorado. At least a section of it. Old Town Fort Collins is worth strolling for shopping and microbrews for those of age.

I'd drive over Trail Ridge Road to Grand Lake, and explore Grand County.

Our favorite resort is Devil's Thumb Ranch. Pricey, but worth it. Lots of activities. Great food. Amazing setting and views.
https://www.devilsthumbranch.com
They have a less-expensive sister property in Winter Park, called Vasquez Creek, which has privileges at the Ranch.

Also, Snow Mountain Ranch is a YMCA property which is low-key and fun.