This is the year to take a drive for a vacation I think instead of going by plane. As you can see, this is a past picture from one of the trip in Yellowstone which is a 10 to 11 hour drive from Denver. If you drive up to Yellowstone, You may want to spend the first night in Jackson Hole and look for some bears and moose in the area and you will love the views of the Tetons. The next day, take the short drive into Yellowstone Park and you will be impress with all the animals like the two above and places like Old Faithful.
I would say stay at least for 5 days and make it a point to watch for people with scopes, they may be watching a Grizzly or a wolf. It could be me!