Urashima Taro and the Turtle

A young fisherman has rescued a turtle. His name was Urashima Taro and the turtle was the beautiful daughter of the master of the seas Ryudzin, who temporarily has turned to an animal. Otohime invited Taro to the underwater palace where he spent some days. They went to view the palace. Otokhime accompanied his guest and showed him the chambers of the palace. Urasima looked around and was admired. But then Uraschima asked for permission to come back to shore. Otokhime handed to Taro a paper box, and ordered him not to open it. Having returned to the village, Taro found out that his absence lasted 700 years. He couldn't find his parents and other people were lived in his house. He was shocked and opened the presented box… What has he found inside?