Downsizing the Giant Pillar
Back in the Main Room, you’ll need to get to 2F. Run back down to this floor and punch out the ice blocks of the Giant Pillar. Take the stairs back up to 3F then roll around the edge. Punch the two ice blocks out at this location too.
Stray Fairy #15
On the bridge right after punching out the ice blocks, look north and down a little bit. You can see the hidden cubby with the Lens of Truth , so get on top of the Giant Pillar and jump off into it. Open the chest to get the Stray Fairy then use the Deku Flower to fly to the side.
The Boss Room
Take the steps back to the top of the Giant Pillar and Fire Punch or Goron Roll through the snowballs. Take the steps to 4F and Goron Roll across the bridge to reach the Boss Room.