In the thousand year door, I don't know how to open the one place with..

The 8 doors below the big thing, they contain the keys. On the 2nd floor to the left, one door has 4 blocks, with 2 different kinds of blocks. Hammer one of them, and then one block, the one in the corresponding spot, will be smashed in the other room on the 1st floor. Hammer the gray ones in each room, then hammer the ones on the pedestals. Hit each blue block in each room by jumping below it. You'll get two keys. Still on the 2nd floor, go to the other door on the left. You'll see 4 skeletons of koopas. Defeat them in this order from weak to strongest. White (Dull Bones)
Red (Red Bones)
Dark White (Dry Bones)
Dark Blue (Dark Bones)
A blue block will appear. Hit it to get the next key.
Still on the 2nd floor, on the right, the first door has nothing special in it. No blocks, enemies, or chests. But if you use Bobbery to blow up the wall on the very right, you'll enter a new room and you'll find a chest containing the key. Same floor, same side, 2nd door, you'll find nothing, just like the room I just talked about, but bigger. Go in the middle and use Vivian's ability. A block will appear. Memorize it's location. Then hit it for the key. On the 1st floor, the 2nd door to the left, there are two red blocks. The chest will appear containing the key. Same floor, left side, first door, once again, nothing. But, all you have to do is just walk into the right side wall. You can just walk right through the wall. Hit the blue block to show the chest. Once more, last time, the last room has nothing. So face the middle and use Flurrie to blow the invisible stuff off to reveal the chest. Then go to the 3rd floor and insert the Star Key that you got from defeating Gloomtail. Then insert all 8 keys in the pillars that arise. After your done with that, go back outside. You can go to the right and then fight 3 old enemies, Beldam, Marilyn, and Doopliss. Then the door on the right will lead you to somewhere different.