Lakeside Laboratory

an old man called Dr. Mizumi works here and researches the life in Lake Hylia in Ocarina of Time. He is similar to the man at the Marine Research Laboratory at the Great Bay Coast in Majora's Mask. Here you can dive in the pool, and the old man will tell you how deep you went. If you touch the bottom, he will give you a Piece of heart.

Also, there is a patch of soft soil outside the Laboratory where you can plant a Magic Bean, enabling access to the roof. The roof can also be accessed by using the Scarecrow's Song.

Trivia

 * If you use the Zora Tunic and the Iron Boots to sink to the bottom of the pool, you will see a cage with a motionless shark.
 * At the bottom of the pool of water are many red rupees.
 * In Twilight Princess, the doctor in the Hyrule Castle Town somewhat resembles the old man inside the laboratory of Ocarina of Time.