Yock Island is a small isle located in the middle of Kauroy Lake near the southern Amestrian town of Dublith. It was here that Izumi Curtis sent the Elric brothers to test their abilities in preparation for apprenticeship under her. They were to survive alone on Yock for a full month without the use of their alchemy. Additionally, she tasked them with figuring out the meaning behind the phrase "All is One and One is All" by the time their month was up. Though isolated, Yock Island seems to be teeming with all sorts of wildlife such as birds, toads, snakes, rabbits, and foxes.
In the 2003 anime, Yock Island was considerably larger, being made up of several large mountains. As well as serving as the place for Ed and Al's trial before Izumi would accept them as apprentices, it is also the place where she sent them after she located the brothers in Rush Valley, claiming they needed time to cool off. On their second visit, Ed and Al are amused by their return, contrasting their first time there with their years of experience looking after themselves as they've traveled. It served as the secret birthplace of Izumi's failed human transmutation, the Homunculus Wrath. For years he lived alone in the forests of Yock until finally being discovered. It also seems that Wrath instinctively imitated Ed after the pair's second arrival, making a black vest and trousers like Ed's from leaves on the island, unconsciously using alchemy. Eventually, the island would go on to be literally split in half by one of Izumi's attacks as she tried to protect Wrath, destroying a large portion of it.
Yock was also host to the battle between the Elrics and Wrath, as well as being the first place they faced Juliet Douglas knowing she was a Homunculus. Supposedly, Dante's manor was located relatively close to this lake.
It is stated by Izumi Curtis that there is no violent wildlife residing on Yock Island. During Ed and Al's time there, they encounter rabbits, foxes, various insects, and fish surrounding the island. Other than that, the island is mostly deserted, with no permanent buildings, wells or sources of power.