Calgary is city of over 1 million people, and traffic is awful. The airport is in the extreme north east part of the city.
In 8 hrs. you might be able to get downtown, have lunch, and then get back to the airport.
The musuem is quite small, and depending on what exhibit is running, not all that great.
There is a war museum. There's a wondeful planetrium/science center. But honestly those show you nothing of the city itself. They could be any city.
There's a spot called Heritage Park, that's built as an old town, but the city itself has grown drastically in the past several decades, and there are very few historical buildings that were retained. The philosophy was rip it down and build. It is dominated by oil company head offices.
The food scene has blossomed in recent history, and so there are numerous outstanding restaurants.
It's a nice city, but the nicest things about it is the areas nearby, outside of the city.