Ice Barriers are objects that serve as blockades, preventing Link from passing.
Ocarina of Time and Majora's Mask
In Phantom Hourglass, Ice Barriers can be found just outside and within the Temple of Ice. These Ice Barriers cannot be broken with Link's Sword. Instead, they require Link to defeat all the enemies in the area, or to solve a puzzle, causing the ice to disappear.
The first such location is found at the east end of the Isle of Frost within the Great Ice Field. The pathway that leads to the entrance of the Temple of Ice is blocked off and Link must defeat six Yooks that are found throughout the ice field to melt the ice. A second Ice Barrier is found right at the entrance to the Temple of Ice. This barrier disappears after Link has defeated the Yook that is guarding the temple's entrance.