From the Super Mario Wiki
Snowflake Shields are circular wooden objects in Donkey Kong Country: Tropical Freeze that display the Snowmad insignia inside a white circle. They usually block access to some Bonus Stages and other secrets, being tied with rope at the entrance of said areas. In order to destroy a Snowflake Shield, the Kongs should first pick up a throwable object or enemy, such as a barrel, Watermelon Fuse Bomb, a Tuff Tucks or a Wild Wendell, and then throw it into the shield; such objects are usually found nearby. Snowflake Shields are first encountered in Canopy Chaos and continue to appear occasionally throughout the game.
This gameplay element, consisting of a wall obstructing the entrance to secret zones, also appeared in past Donkey Kong Country titles, although under various appearances and with no definite names. They could be broken with barrels or Rambi the Rhino.