If I remember correctly (been a while since I first got this keyblade) you must have access to a part of the Bizarre Room. Also, you must have the ability to unlock White Trinitys (iirc, you must beat Riku the first time in Hollow Bastion). It'll be in this part where there are these lamps. read more
Also, you must have the ability to unlock White Trinitys (iirc, you must beat Riku the first time in Hollow Bastion). It'll be in this part where there are these lamps. Light them, and a picture will show of the Lotus Room. read more