Piano Keyboard Quest

To get to Niffleheim, you have to jump the Bungee jump at Umbala or walk past field to head to Niffleheim.
(The Bungee jump is the shortest and quickest way though.. unless you keep on dying :P)

Once in Niffleheim, talk to Arego (Niflheim 224 243).

He'll drain your HP, so be sure to have restorative potions ready or make sure you don't have a mob of monsters following you.

You'll get your first piano keyboard.

Head over to Niflheim 187 241. Enter the house and talk to Greyryu or Crayo.

Once you talk to him, he'll tell you song:

Mountain sunset to the west
Where the purple dusk falls
Surrounded by beautiful melody
You become the key that ignores its master

Afterwards, he'll ask you for a line, key it in properly and you'll receive your second keyboard piece.

Head back to the Inn (Niflheim 188 212), (if you Bungee your way to Niffleheim, the Inn would be the place you landed) on the first floor, Cushca Sina will not be happy about his business in the afterlife. And he'll throw away a keyboard piece.

Go outside, walk over to Niflheim 208 103 around the tombs. Wait for a pop-up to appear. You'll need to pick up the keyboard piece.

Walk away and move towards the place again to get the second pop-up. Again, pick the keyboard piece up.

Now walk over to Niflheim 169 71. You'll get a pop up similar to the first one you received earlier.

Again, pick up the last keyboard piece.

Now head over to the Witch Tower (Niflheim 254 191). (Remember though that her tower sits at the zenith, so you have to find the floating stairs to get there.)

Once you're inside, find your way to the second floor, and talk to the piano.

Moving southward, (you don't really need to walk down the carpet) you could come across a trap door.

In doing so you could get teleported to the Witch's Room.
If you talk to her, the Witch will warp you back to Umbala.

[END]

Note: Both of these quests are required to proceed with the 2nd part of the Sign Quest.