The Magikarp Caverns are a series of caves in Naljo where people can worship Magikarp. They are located in the north-east corner of Laurel City, and do not have their own location name on the map.
The entrance is blocked before the player has the Charm Badge. Visiting this location is required to progress, as a Magikarp worshiper blocks the way through Laurel Forest until the Caverns' trial is completed. The caverns also provide access to the Tunod region (Route 87) later in the game.
There are no trainers here, and no wild Pokemon spawn. However, there are items, one of which requires HM04 (Strength) to reach.
The rocks in the cavern are arranged to resemble a Magikarp when seen from above, with various pathways and ladders leading eventually to a pool in the center. The Tunod region can also be reached via the north of the cavern, but an old man blocks the path until the player matures as a trainer.
Speaking to the old man beside the pool will allow the player to begin the trial in the form of a Magikarp. Once this is completed, the way through Laurel Forest will be unblocked.
In the center of the caverns, above the pool and the old man
Via a ladder blocked by a rock (requires Strength)
Main Cavern Walkthrough
Map of the main cavern, with labels for both ladders and items.
Once the trial is begun, the player will be turned into a Magikarp and must complete a navigation puzzle consisting of water rapids and whirlpools. Moving onto a "rapids" tile will propel the player forwards until they reach another rapids tile or calm water. Whirlpools act as portals, transporting the player to another whirlpool elsewhere in the caverns.
The goal is a whirlpool which transports the player into the final cavern where the old man is waiting. There are also two item balls that can be picked up along the way.