Fake Namek is a planet that only appeared in the anime. Its disguised appearance has green sky and lakes like the real Namek, but also deserts, forests, caves, and castles. Its true appearance is a dark, cloudy area full of man-eating monsters. Raiti and Zaacro were trapped on the planet. A fog around the planet makes it inescapable unless the Stellar Winds are near.
In the manga, Gohan, Krillin, and Bulma go straight to Planet Namek upon their departure from Earth. In the anime, however, the "Dragonball Gang" encounters two obstacles. The first is an invisible spaceship full of aliens that mistake them for the henchmen of Frieza. The second is the fake Planet Namek.
Upon landing on the fake Namek, they were knocked unconscious. Raiti and Zaacro found them and took them to a building, creating illusions of a Planet Namek after reading their minds with their antennas. Why the fake planet looked like the real Namek on the outside when Raiti and Zaacro hadn't read their minds yet is unknown, but it might be a special feature of the planet itself.
Raiti and Zaacro disguised themselves as Nameks and constructed some quests to find the Dragonballs. The first Dragonball was found by Raiti under a boulder in the middle of a lake. The second was inside the mouth of a skull, in a coffin in an underground cave. The next three were more of a challenge. The third was taken by a monster dinosaur, which fell into a lake full of acid forcing Gohan to go in with a specially designed suit and get the Dragonball, escaping the lake with a Kamehameha. The fourth was inside a tornado, where Gohan jumped into it, grabbed the Dragonball, and destroyed the twister with a Kamehameha. The fifth was inside a giant's castle above a forest, where the forest floor came to life in the form of tree birds that took Krillin, Gohan, Bulma, and Zaacro (who takes Raiti's place at this time) to the castle. The Dragonball was on the giant's earring, and they got it off, but unfortunately the giant woke up! Krillin and Gohan fought the giant, causing some considerable damage to him (and the giant being one of the only four characters (the others being Frieza, Cell, and Buu) to be hit directly by Krillin's Destructo Disc, but he might not count because he was an illusion), but despite losing a hand he was still able to fight back, until Bulma and Zaacro rescued Krillin and Gohan inside a toy airplane.
The sixth Dragonball was frozen inside an ice cave. Krillin and Gohan slowly melted the ice with energy waves to get the Dragonball, but the cave began to collapse (Raiti and Zaacro might have been the true reason behind it) so they sledded down the tunnel on a block of ice. Raiti and Zaacro sent a boulder after them, but they escaped the tunnel. The seventh Dragonball was inside a building, but the man-eating monsters (outside of the illusion) attacked Gohan before he could get it. Raiti and Zaacro revealed their true forms and intentions, and the illusion disappeared. Bulma left to stall Raiti and Zaacro, who intended to steal their ship, waiting until the Stellar Winds came so they could escape. Just as they were inside, Krillin and Gohan, having dealt with the man-eating monsters, stopped them and knocked them down. As the Stellar Winds were almost gone, Krillin and Gohan didn't have time to kill them, so they and Bulma got into the ship and left the fake Namek through the Stellar Winds. Raiti and Zaacro were left on the planet, and presumably are still there by the end of Dragonball Z.