當然是 "A surprising day." : ) 因為surprising 是用來指 "事情" 很驚人的 (原意為 : "令人"出乎意料的) It's surprising. (這真令人出乎意料) 而surprised 是用來形容 "人" 很驚訝 (原意為 : "感到"出乎意料的) I feel surprised.(我感到驚訝) 而其他像excited / exciting, amazed / amazing...等都是這樣的用法! PS. To one's surprise, S+V. (令某人驚訝的, S+V.)

A surprising day. If you said, a surprised day, that would imply that the day was surprised by something. Where, a surprising day, implies that you or someone else were surprised by something on that day.

A surprising day is correct meaning that things happened that you didn't anticipate.

the surprising day~ or someone feel surprised on that day, 大概就是这个意思