A History of Masks
After Link completes the Fortress of Winds, he begins his quest to look for the Water Element. Link can use the Ocarina of Wind to warp to the Lake Hylia Wind Crest, where he can find a Minish living here. Link learns that the Element is located within the Temple of Droplets, but the only living person to have entered the Temple of Droplets is Librari. Librari lives within the Royal Hyrule Library.
In order to reach Librari, Link must acquire the three missing books that have been checked out from the library, but not returned. The third book is A History of Masks. The book can be found at Mayor Hagen's Lakeside Cabin in Lake Hylia. In order to reach the Cabin, Link must travel to the north portion of the Minish Woods. From there he can use the Mole Mitts to dig into a cave that eventually leads to Lake Hylia. Just north of the Cabin, Link will need to use the Tree Stump to shrink down to Minish size. Here, he can then cross the small pond and enter the north side of Mayor Hagen's Lakeside Cabin.
Inside the Cabin, Link must use the Power Bracelet to push the large shelf to the right, granting him access to a small staircase. From here, Link can climb up and push the book off the shelf. After collecting the third and final book, Link can return it to the library.
A History of Masks inside of Mayor Hagen's Lakeside Cabin