Depends how old they are, for what purpose and when they are coming.
the Calgary Tower is always interesting.
Fort Calgary usually has a lot of art and craft shows, with some heritage.
The Glenbow Museum is... well a museum, and downtown is always home to some colourful variety of shops, people, restaurants.
Heritage Park is an amusement park focusing on History...
During the summer, you could go to the Stampede (festival celebrating westernness) or Calaway Park (amusement park).
If they were staying for longer, you must take them to Banff if they're willing to get out of the city and embrace nature. Very cute little shops and the mountainside tourist town feel.
But if they're grumpy, stubborn, and old, you might as well drop them off at Chinatown, and let them play Mah-Jongg.
... Have fun?