You got stuck in airport due to a long layover, flight delay, missing connecting flight or just want to chill before your next flight and you are only travelling on economy class without premium frequent flyer membership. Most people will be in this situation unless you fly for business a lot. So here is a membership to get: Priority Pass.
What this membership provides you with is 2 visits to any of their 850+ airport lounges around the world per calendar year for free. I got this membership card for free through 2 credit cards which give me 2 separate Priority Pass cards for 4 visits to their airport lounges per year. Please note that you shall bring physical Priority Pass membership cards to airport lounge.
To find out which airport lounge is available under Priority Pass, you may use their application for Android and iOS.
Here are some screenshots from Priority Pass application.
This application is available for FREE without ADs on Android Google Play and iOS App Store.