Answer: On such a beautiful day
An absolute phrase is a phrase that modifies a sentence, but is not connected to the sentence by a conjunction. They are often set apart by a comma and are not essential to the meaning of the sentence.
In this case, "on such a beautiful day" modifies the sentence by providing more details about the day at the beach. However, the information is not crucial to the sentence. Moreover, it does not represent a full sentence with a subject and a verb.
