There are lots of national parks nearby and that should be a decent time of year to spot a reasonable amount of wildlife.
Caribou Ranch Open Space is one where we spotted an entire herd lounging around.
Its west of Boulder.
Heading directly west from Denver on i70 are lots of natural areas
And once you get to Loveland you drive right through the middle of the ski area (neat tunnel) and can continue to a lot of neat little towns & lots of other ski areas most of which are in various national forests
Its a beautiful drive even if you see nothing else
@ChristianSchmitz I am even considering doing a long drive to north and visit a few things there like the Mount Rushmore National Memorial.
That might make for a long day - its a 5+ hour drive each way from Denver
Might want to overnight in South Dakota
EDIT : Who knows - MAYBE we'll luck out and the Colorado Avalanche will make the NHL playoffs which would be starting about then
The Bronco's wont be playing
Maybe the Rockies or Nuggets will be - but their schedules arent out yet