The Book of Seals is a quest item from The Legend of Zelda: Oracle of Ages. This book is given to Link by an Old Man in the back of the Eyeglass Isle Library in the present. It can then be taken to the Past and placed on the pedestal in the back room of the library. Reading the book will instruct Link how to navigate the invisible floor to the next book, and eventually to the Old Man in the middle. Upon reaching the Old Man, Link is rewarded with a vial of Fairy Powder.
The floor is completely intraversable unless the book has been opened and read on that, and all attempts to proceed. That is, every failed attempt will send Link back to the start, closing the book and erasing the floor until Link reads it again.