Book a round-trip flight on Sun Country to London by April 15, and receive a free round-trip flight to anywhere Sun Country flies in the contiguous United States. 

To qualify, you must book the London trip through Sun Country Airlines or a London Package through Sun Country Vacations for travel between May 27 and September 4 (the full duration of the airline's seasonal service to London).

There's loads of fine print (black-out dates, additional taxes and fees, etc.), but still a great deal for anyone planning a trip to London this summer. Sun Country's seasonal flights to London's depart every Friday from MSP and arrive in London-Gatwick on Saturday morning.

Return flights from London depart every Sunday.

For more information, go to Sun Country and click on "royal offer on purchase to London."