Upon entering the dungeon with Team Charm, the player meets numerous Unown and beating some of them gains the player a stone, with the Unown's letter on. To get into Regice's room, the player needs the I, C and E stones. To get into Regirock's room, the player needs the R, O, C and K stones. And to get into Registeel's room the player needs to obtain the S, T, E, E and L stones. After defeating three legendary golems, the teams can go through Aegis Cave and battle with Regigigas along with 4 Hitmonlee and 4 Bronzong. After the dungeons is completed for the first time, the Concealed Ruins are unlocked.
The Regi's cannot be recruited on the first visit. Prior to unlocking Concealed Ruins, if the player exits the dungeon (either via an Escape Orb or by being defeated), the player must rebattle the Regi's on subsequent attempts of the dungeon.
Aegis cave is located at the west side of the southern tip of the mountain area on the Wonder Map.