The Legend of Zelda: Majora's Mask

This part is kind of confusing, I agree. You need to go back out of that room, into the room across the hallway.
Activate the crystal switch in the room, and the floor will rise to become a
crushing ceiling. Use the Bunny Hood or the Goron Mask to cross to the east
end of the room as quickly as you can. Stand near the door and wait for the
ceiling to crash back down. As Deku Link, activate the crystal switch next to
the door, causing the crushing ceiling to rise again. Use one of the Deku
Flowers near the door to blast up to the tall pillar on the south side of the
room. Step on the switch as Hylian Link to activate it, then jump back towards
the door on the east side of the room. Go through it.
Look to the north as you enter the room to see a small ledge with a switch on
it. Dive into the Deku Flower and float to that platform, and step on the
switch. The door on the east side of the room will open. Look to the east and
kill both of the Big Skulltulas you can see hanging from the ceiling. Activate
the Lens of Truth to see an invisible platform to the southeast; jump to it,
then keep jumping east along more platforms to the east side of the room, and
go through the door there.
There are two Blue Bubbles in this room. If you haven't encountered them
before, then keep in mind that touching them will curse you and prevent you
from using your sword. You can use the Song of Storms to end the curse,
though. Break the Bubble's shields by walking into them with your own shield
raised, then defeat their skulls. Head east to the end of the hall and go through the doorway and up the stairs.
Run forward and go through the door to reach the north end of the castle roof.
Climb up onto the rubble in this area, and then onto the wall. Be careful you
don't fall here, or else you'll have to go all the way back through the
interior of the Castle. Look to the northwest to see a Crystal Switch. Shoot
it with an arrow, and the pillars of flame on the columns to the north will
reside. Jump out to the top of the columns and change to Deku Link. Use the Deku
Flowers on the columns to the head to the column on the far east of the area,
claiming a Piece of Heart. Drop back down to the courtyard floor and return to
the roof of the Ikana Castle. Back on the roof, climb back onto the rubble and return to the wall of Ikana
Castle. Run south along the perimeter of the wall until you are above the door
leading into the castle. Look to the west here to see a small ledge above the
doorway. Jump down on it and dive into the Deku Flower. Float from the Deku Flower to the switch on the column on the west side of the
area. Stand on the switch, and a new opening will appear on the south side of
the area. Jump down from the column and re-enter Ikana Castle, and voila - you now have sunlight with which you can dissolve the block.

It's been a while since I did this part, but you need a Powder Keg (for later). Once you have that, return to the room and look for iced eyes on the columns. Shoot Fire Arrows at them and exploring should be easier from there. Also, you'll need the Lens of Truth later on.

You must get on top of it and blast a hole with a Powder Keg.