Step 1: Understanding the Concept:
A tourist city is known mainly for drawing visitors, through religious, historical or scenic importance. Some Indian cities are famous for tourism while others are known chiefly for industry or trade.
Step 2: Check each city.
Mathura and Varanasi are major religious pilgrimage centres in Uttar Pradesh, visited by huge numbers of tourists every year. Shimla is a well known hill station and tourist resort in Himachal Pradesh.
Step 3: Why Kanpur is the answer.
Kanpur is chiefly known as an industrial and manufacturing centre, famous for leather and textile industries, not as a tourist destination in the way the other three cities are.
Final Answer:
Kanpur is not a prominent tourist city among these four.\[ \boxed{\text{Kanpur}} \]