This dungeon can be unlocked sometime after releasing Manaphy. You team up with Team Charm
and the Guide to explore for treasure in the dungeon. When you first enter, you'll see a
Stone Tablet in the middle of the room. You'll talk a little with Team Charm and some of
the members of the guide. It will say that "There are oddly shaped grooves in it."
Right after, there will be markings of an Unknown I, C, and E. (I'm not sure if the puzzle
is the same for all games) (If not, look for the stones of the Unknown on your game) You
will then be asked to close your eyes. Don't do it yet.
Continue on into the dungeon. The enemies are randomly put on each floor. You'll find
Unknown, the 4 Regi's, and the evolution line of Machop and Zubat.
Unknown will randomly drop a stone with a letter that will be accordingly to the type of
letter the Unknown is. Go to "Others" on the menu and pick Recruitment Search. Look for
Unknown C, I, and E. If one of them is on the floor, look for them until you defeat it and
get the stone. Do this for the next floors.
There are only 3 Floors for this place. If you don't get the stones you need, you'll have
to go through the dungeon again. Keep doing this until you get all 3 stones.
When you have all three stones, go to the stone and say yes when it asks you to close your
eyes. A stairway will appear! Go down it. You'll go into Regice's Chamber!
Now, you'll engage into a fight with Regice, one of the legendary Golems. His weaknesses
are Fighting and Fire Type Moves, but I recommend to bring Fighting Type Moves because the
rest of the Regi's share the same weakness. When you defeat it, you'll go on to the next
puzzle.
The next tablet will have the Unknown letters, R, O, C, and K this time. Just use the same
method I said for the first puzzle. Go and continue on to Rock Aegis Cave. When you have
collected all of the Unknown stones you need, close your eyes in front of the stone
tablet. Go through the next stairway that appears. You'll go into Regirock's Chamber.
Again, just use Fighting Type Moves.
After you defeat Regirock, you'll find another stone tablet. This time, you have to look
for the letters S, T, E, E, L. Do that and close your eyes in front of the tablet. Another
stairway will appear. Enter it and you'll go to Registeel's Chamber. Just use Fighting
Type Moves again. After defeating Registeel, you'll enter Aegis Cave Pit and meet Team
Charm. The next part is only 5F long.
On the last floor, you'll meet Team Charm. The statues of Regigigas, the 3 Hitmonlee's,
and the 3 Bronzong's will come alive and you'll team up with Team Charm to defeat them!
Regigigas is weak against Fighting Type Moves
Bronzong against Fire Type Moves
Hitmonlee against Flying and Psychic Type Moves
You won't need my help anymore for this dungeon so good luck on the rest of your journey!