How do I search for multiple airports in a city?

This option is available for Round Trip, One Way and Multi-City search. By default it is enabled.

This gives you the ability to search for flights to/from other airports in the same city as specified in the "From" and "To" location fields. This gives you a broader range of search results, allowing you to find potentially cheaper fares for your traveler.

You can disable this option for each flight search. Additionally, the default value can be changed/configured in the admin setting.