No, you cannot access a Priority Pass lounge without a valid, same-day boarding pass. Priority Pass is a membership program that provides access to over 1,500 airport lounges worldwide, but it is strictly for travelers. When you arrive at a lounge, the reception staff will ask to see your Priority Pass (either the physical card or the digital QR code in the app) along with your boarding pass for a flight departing from that airport on that specific day. This rule applies regardless of whether you are flying Economy, Business, or First Class, and regardless of the airline you are using. In most cases, you cannot access lounges upon arrival at your destination because you must pass through security and immigration, which takes you out of the "airside" area where the lounges are located. The boarding pass is the primary proof used by the lounge to verify you are an active traveler and to bill the visit correctly to your membership or credit card issuer.