A Curious Curio is a music from the Shovel Knight Pocket Dungeon Original Soundtrack. This is the theme of the cutscene after clicking the Adventure option from the main menu for the first time.
In this cutscene, Shovel Knight is seen sleeping by a campfire when a gift shows up. Intrigued, he opens it to find a strange box. After examining it for a moment, the box activates and sucks him inside.