H, the Tundra Wilderness Tour is one of 3 possible ways to tour inside of Denali NP. You may do other excursions or hikes in Denali, but the touring is the big reason you're going there.
There is 1 road through the park and it is largely closed to private vehicles...the lone tour operator licensed for this has 3 options that travel in and out on this 1 road and the difference is largely the distance into the park. The natural history tour at 3 hours does not go far enough in to get to the really amazing locations ... both scenery and wildlife. Wildlife can be random, but most people see very little on NH tour...when we were there, stories were about seeing a moose's antler, which could have been a bush, the people weren't sure. On the Tundra tour, we got amazing scenery and grizzly, caribou, moose, and Dall sheep walking around us and around our bus.
Denali is usually a highlight and you spend a long time in transit, so Karen and many of us here will always recommend you choose 1 of the 2 other options: Tundra Tour or the shuttle system. Shuttles allow you to pick your distance and you'd want to go to Eilson Visitor Center. Tundra tour stops short of this, although it is elongated to get closer to Eilson when Mt. McKinnley is visible (not too often). Tundra tour is much more expensive than shuttles and includes a small largely inedible lunch. Shuttles let you get on and off at various spots for hiking/walking and although they are not guaranteed to give you as much commentary as a tour, most people are not disappointed by the tour-like nature of these tours.
On a cruisetour to Denali, either Tundra or Natural History is usually included in the cost (because you've already paid for the tour, shuttles factor out of the mix). So, Karen wanted you to check to see which one you have. You should be able to find these pre-paid activities on any of the literature about your cruisetour or on your itinerary. If Natural History, consider picking another tour that will allow the tundra tour and/or consider upgrading to the tundra tour (if there is space and if time is available on your tour). All too many learn the difference between these 2 very different option only when its too late.