What Terminal is Southwest at DIAAt Denver International Airport (DIA), Concourse C is the base of operations for Southwest Airlines. Located between Concourse B and Concourse A, Concourse C is one of DIA's three middle concourses. Concourse C houses the ticket booths, check-in kiosks, and boarding gates for Southwest Airlines passengers. The efficient design and state-of-the-art amenities of Denver International Airport make it easy for passengers to move between the terminals and concourses.