You can buy tickets on the Gardner museum website ahead of time or at the door. They have a QR code to scan and buy there. Keep in mind the tickets may be limited, but I don’t think that will be a problem unless you are planning to go at peak hours.
Their website says that advance tickets are required - purchased online (as of Aug. 7, 2021). You choose a half half hour window for your arrival. Masks are required.
On line
You go to their website. It’s really easy but they are limited still with Covid.
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