The Kalm traveler is a non-player character in Final Fantasy VII found in the rightmost house in Kalm. Later on he will accept trades with the player for three items he is searching for: the Guide Book, the Earth Harp, and the Desert Rose. Kalm traveler does not exist in the original Japanese release, as the superbosses Emerald and Ruby Weapon are not included in that version.
The Kalm traveler is not named in-game, but is referred to as the "Kalm Traveler" in the BradyGames Official Final Fantasy VII Strategy Guide as a sidequest and in item info sections. Japanese guide books do not refer to him in a consistent way, with the sidequest referred to as the added International items, and only mentioning the items can be exchanged in Kalm in the item info.
The Guide Book can be traded for the Underwater Materia, which lets the player fight Emerald Weapon without a time limit. It can be morphed from the Ghost Ship in the Junon Underwater Reactor, in the glass tunnel area on the sea bottom. The Kalm traveler only gives out one Underwater Materia per game, even if the player has multiple quantities of Guide Book. The Earth Harp is won from Emerald Weapon and can be traded for Master Magic, Master Command, and Master Summon Materia. The Desert Rose is won from Ruby Weapon and can be traded for a gold chocobo. Both the Earth Harp and the Desert Rose are unique items that the player may wish to conserve, being that only one of either exists in the game normally. After handing them in, the Traveler leaves the house to journey to parts unknown.
If there is no room in the stables by the time the player acquires the gold chocobo from the Kalm Traveler, the chocobo will stay at his house and the player can come back later for it. If the player uses a cheat or a hack to get more than one Earth Harp, the old man will continually give them more Master Materia unless the player has not picked it up already. If the player does not pick up the Materia, it just bounces in the air instead of him throwing another one.