From the Super Mario Wiki, the Mario encyclopedia
Spinning Platforms, also referred to as trapdoors or trap doors, are simple mechanisms resembling floor tiles. They are present in Donkey Kong Country Returns, Donkey Kong Country Returns 3D, and Donkey Kong Country: Tropical Freeze, being noticeable by the empty gap underneath them.
If pounded, Spinning Platforms start rotating around their axis for a short time, allowing the Kongs to fall under them. They usually lead to hidden underground chambers or Bonus Areas, where the characters can find secrets. Spinning Platforms are semi-solid, meaning they can be walked on as on solid ground but can be crossed from beneath. While spinning, it can defeat any enemy that comes into contact with it.