If you have some extra time/want a side quest and the weather isn't adventurous, Ouray in extreme western Colorado is amazing and can easily be combined with the Black Canyon of the Gunnison (someone posted about that already). Hot springs! Gorgeous mountains!

Ohhhh hot springs do sound divine, especially after hiking days

Also, all National Parks and big state parks have a visitors' center that's very well-equipped to deal with "what can we do in a car/what really easy walks do you recommend?" They pride themselves in having something for everyone no matter what their abilities and interests. So always start there.