Qatar Airways offers a stopover program on some of its selected flights. Moreover, this service gives one the chance to explore Doha while waiting for their connecting flights. With the help of the Qatar Airways Stopover Program, travelers can stay in Doha for up to 96 hours at reduced rates and are allowed to enjoy the city during the layover. However, these features can be used once for each ticket. For more details on this, contact the customer service of Qatar Airways or check out the blog linked above.