The Valley (Japanese: けいこくValley) is one of the six major areas of Pokémon Island, and like its name suggests, it is a valley with a whitewater river flowing through it. The rapids are fast-moving, with numerous drops and twists. At a fork in the river at the end of the Valley, a floodgate seals off a lagoon where a tropical island hut can be found. The player must use Pester Balls and a Squirtle to knock a Mankey onto a button to open this floodgate. When the player first visits this lagoon, they will find Professor Oak, who informs them of his discovery of Pokémon signs.
Thirteen different species of Pokémon can be photographed in the Valley. Many of the Pokémon living in the area are aquatic and Water-type Pokémon, ranging from the common Magikarp to much rarer Pokémon such as Dratini and even Dragonite. There are also playful Squirtle that swim and play within the river and on its banks.
When the player enters the course, brown shells can be seen bobbing in the water. Hitting them with an item will knock them forward. If the player angles it correctly, they will land on the shore and pop out, revealing themselves to be Squirtle. They can be seen near the end of the course as well, with all but one skidding up a large mound. The last will roll up if the player hits it with a Pester Ball.
There are three Mankey throughout the stage. The first is seen early on, yelling at the player from a distance in front of Mt. Dugtrio. When the river first starts getting very rapid, another can be seen on a ledge on the left side of the river, also yelling at the player. The last one is on top of a large mound, yelling at the player as well. This one, however, can be knocked down by hitting the Squirtle at the base of the mound and making it skid up the mound; aiming it correctly will knock it right into the Mankey. This puts Mankey in a close spot for pictures. A Pester Ball will cause the Mankey to fall on a switch, opening up the route to a little pond.
There are three of these, buried deep underground. The player can see them briefly from a distance before they burrow underground, but the only way to get a decent shot of them is to knock down the Geodude clinging to the rock wall with Pester Balls. They will fall, and the shock of them hitting the ground will drive out Sandshrew.
Like Sandshrew, Sandslash burrows underground before the ZERO-ONE can come close enough for a good shot. Knock down the two Geodude, and the Graveler above will fall, causing Sandslash to leap out of the ground. Professor Oak can be impressed by a shot of Sandslash getting ready to dig back down.
One can be found with the Geodude and must be knocked down by knocking the two Geodude near it down in rapid succession. Three Graveler are also seen sleeping later on the course. Playing the Poké Flute will wake them up, and they will do a tribal dance.
If a Magikarp splashing around in the beginning is knocked out of the water, it will splash on land towards a Mankey, who will send it flying with a big punch. The player will encounter this Magikarp again later in the stage, flopping around on land. Hitting it with a Pester Ball will make it flop back into the water and up a nearby waterfall, evolving into Gyarados.