For its western half, Route 3 is a split-level route. Heading east from Pewter City, the player encounters a small clearing with some natural obstacles that create a fork in the road, forcing travel north or south, of which the south path curves east and leads to a group of rocky pits (Generation IV only) and a dead end. In order to progress, the player must turn north and then east along the northern half (which, in GenerationsI and III, is packed with Trainers). At any point, the player can jump the ledges located here to access a middle section of the route between the two ledges. Most of this middle area contains items, as well as another Trainer waiting for battle. By hopping a ledge again, the player is able to travel west toward the pits and then north back to the clearing at the start of the route.
East of the second section of the ledges, the route curves south and then east near a large patch of tall grass containing wild Pokémon, which takes up most of the area. This patch, which contains another Trainer, follows the route until it turns north ahead of a hill. (In Generation IV, the player can go through the grass to reach a ledge running along the southern edge of the route.) From this point, the route makes a backward "S" curve, turning east past the hilly terrain, south past another ledge that leads the route to a large clearing, east again, and finally north, passing a second patch of grass near the end, which has a fence around it as well as a signpost for directions. (In Generation IV, however, the eastern half of the route only goes south-east and does not bring the player north until the second patch of grass.)
The only obstacles along the remainder of the route are a few ledges on either side, which are easily bypassed as the player proceeds north towards the mysterious Mt. Moon cave and Route 4 beyond. Beside the entrance to the cave is a Pokémon Center, one of only two in Kanto that is not located in a populated area (the other one is on Route 10 at the north entrance to Rock Tunnel). In Generation III, Fly is able to return the player to this location instantly, but not in any other Generations. In the Pokémon Center, a man attempts to scam Trainers by selling them the laughably common Magikarp for relatively high prices.
The only changes along Route 3 between these two Generations are cosmetic, such as the reconstruction of the surrounding landscape. The barriers on either side of the route are removed in the Generation III remakes, while the large patch of tall grass in the center of the route becomes considerably smaller. Also the set of trees have been removed in Generation I and have been replaced by a rocky mountain setting. Other than this, most of the route remains the same.
Many changes were made to Route 3 in Generation II. First, the route was shortened significantly. Also, the number of Trainers along the path was reduced to four. Similarly, the size of the grass patches were reduced by nearly 50%.
Traveling east from Pewter City, the route passes two barriers on either side of the road, and cuts to a clearing that creates a fork in the road, and allows travel north or south, with south curving around eastern and then leading to a dead end. In order to progress, Trainers must turn north after the route opens up and progress east along the northern half. For its western half, Route 3 is a split-level route, so at any point, Trainers can jump the ledges located south of this path, to access a middle section of the route between two ledges, and then again, so Trainer are able to travel west which curves north back to the clearing at the start of the route.
East of the second pair of ledges, the route curves south before returning east near a small patch of tall grass. The size of the tall grass has been reduced by about half. This patch follows the route until the path turns north ahead of a hill. From this point, the route makes a backward "S" curve, turning east past the hilly terrain, south past another ledge taking the route to a large clearing, east again which travels across the clearing, and, finally, to the north, passing the second patch of grass which has also been reduced in size, which has a fence as well as a signpost, which gives out directions.
Part of Route 4 has been combined with Route 3 so now only one route connects Pewter with Mt. Moon, however, the Pokémon Center is no longer there. There are no obstacles along the remainder of the route as it proceeds north towards Mt. Moon.
The meteorites located at the southwest end of Route 3
In Generation IV, the route is different from other generations, with some area changes, as well as major aesthetic features enhanced, including depth and sprite changes. The trees removed in Generation III return, and the east area of the route changes too. Hills, rocks, and smashable rocks are added near Mt. Moon, now part of this route like in Generation II. An additional area at the southwest end of the route allows players to change their Deoxys's current form by interacting with different meteorites. Also, a new hill is placed south of the tall grass.
For its western half, Route 3 is a split-level route. Heading east, Trainers must turn north after the route opens up and progress east along the northern half. The southern half of the route is only accessible by hopping down ledges that will lead Trainers into the paths of more rival Trainers. East of the second pair of ledges, the route curves south before returning east near a large patch of grass containing wild Pokémon. This patch follows the route until the path turns north ahead of a hill. From this point, the route makes a backward "S" curve, turning east, south, east and, finally, to the north, passing the second patch of grass on the route. There are no obstacles along the remainder of the route as it proceeds north towards Mt. Moon. Just before the entrance to the cave, there is a Pokémon Center.
Three unique items have also been scattered around the place, including a Big Root, located near a Firebreather; a Star Piece, located near the meteors; and a Hyper Potion, hidden near the Pokémon Center. The number of Trainers along the path has been increased to eleven. The Pokémon Center at the entrance of Mt. Moon returns but the area around it was reduced significantly in size.
Route 3 appeared in Gyarados Splashes In!. Red first encountered Misty on this route, fighting a rampaging Gyarados. With the help of Red's Saur, the Gyarados was stopped and eventually caught by Red. Afterwards, Misty told Red that the Gyarados was actually hers, having gone missing some time earlier and returned raging mad.
Although there are seven breakable rocks around the Pokémon Center in HeartGold and SoulSilver, there are no wild Pokémon to be found under them. As a result, Route 3 is the best place for collecting items found via Rock Smash.
In all languages, when Bug Catcher Colton first approaches the player, he says "I saw you in Viridian Forest." and upon defeat he says "You beat me again!" However, there is no Bug Catcher named Colton in Viridian Forest. In Generation I, since Trainers other than the rival, the Champion, Elite Four members and Gym Leaders are unnamed, he could reasonably be one of the Bug Catchers battled in Viridan Forest, but his lines were not adjusted in Generation III when his name made it apparent he was a different Trainer.
Route 3 is the scene of a famous quote among Pokémon fans, where Youngster Ben exclaims, "Hi! I like shorts! They're comfy and easy to wear!" Further along in the route, another Youngster exclaims "Hey! You're not wearing shorts!"
In Humilau City, a Lady will make a reference to Ben, saying, "This dress is comfy and easy to wear..."
On Kalos Route 5, Youngster Keita will say the exact same words as Ben.