The Hidden Land (Japanese: まぼろしのだいちPhantom Land) is a Dungeon in Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness and Pokémon Mystery Dungeon: Explorers of Sky. The Hidden Land has 15 floors, and the Hidden Highland has eight. The Hidden Land was passed down in oral legends for a long time, but nobody had ever found it. It is an area located in a gap in time, or between the split of a second, as Lapras put it. It was hidden to prevent anything happening to Temporal Tower, home to Dialga, controller of time. If the flow of time was disrupted Temporal Tower would collapse. This would cause time to stop, and the planet would be paralyzed, in a shroud of darkness. The only key to entering this land is the partner's Relic Fragment.
When Torkoal, the town elder, is asked about the Hidden Land at the Hot Spring, he mentions that one needs "proof" to enter, but then forgets. He comes the next day and tells the guild that the proof is of a strange certain marking. The player remembers that their partner's Relic Fragment has a strange pattern on it, and tells him/her to show it to Torkoal. He is astonished when he sees the needed pattern on the Relic Fragment. When the fragment is brought to a larger marking in Brine Cave, the two react and a light shines from the large marking, summoning Lapras, who will ferry Grovyle, the player, and their partner to the Hidden Land. At the end of the Hidden Land is the Old Ruins, where the Rainbow Stoneship lies, as well as Dusknoir, who ambushes the party with his Sableye.
No Pokémon, excluding Grovyle, the player, the player's partner and Lapras, can enter the Hidden Land. Ironically, this means that if the player recruits Dialga, it will not be able to go back to Temporal Tower. Even on post-game visits, the player must be the leader, and the player will be kicked out and lose items and money if the partner is knocked out.
The floating island explored during the player and partner's visit to the future appears to be the future version of the Hidden Land, due to the Temporal Tower being there and the two landmasses having the exact same shape. Presumably, Dialga's maniacal behavior caused the Hidden Land to become visible to all.
The Hidden Land appeared in Pokémon Mystery Dungeon: Explorers of Sky - Beyond Time & Darkness, where Team Poképals and Grovyle arrived there with Lapras. Once they arrived at the Old Ruins, they prepared to use Rainbow Stoneship to get to the Temporal Tower, but were ambushed by Dusknoir and a group of Sableye before they could do so. Dusknoir stole the Relic Fragment needed to activate the Rainbow Stoneship and intended to return to the future through a time portal, but was stopped by the combined effort of Team Poképals and Grovyle. In order to prevent Dusknoir from stopping Piplup and Chimchar, Grovyle took Dusknoir with him back to the future, leaving behind the Time Gears before doing so. After this, Team Poképals activated the Rainbow Stoneship and headed to the Temporal Tower to stop Primal Dialga.