POKEMON EMERALD UNLOCKABLES
Sea Cave
Sea Cave is a cave found underwater after defeating the Elite four. The legendary Kyogre thrives in the Sea Cave. It is on Routes 105, 125, 127, or 129. You must go to the Weather Center. He will tell you where Kyogre is located. However, if you take too long finding it, it will move on.
Opening the Regis caves
You must first get Waillord and Relicanth. Then, go to Pacifidlog City. Go left into the currents. You will see a square in the water. Dive down then go into the cave. Get to the end of the cave. You will see Braille on the wall. While in front of the Braille, dive up. You will be in a cave. Go to the end of the wall and use Dig to enter the next room. You must have Waillord first in your party and Relicanth last. Then, read the Braille. The ground will shake and the caves will now be open. One is in the desert and the other is in the water in near Deleford Town.
Safari Zone
The Safari Zone is the same as the one in Pokemon Ruby and Sapphire. The only difference is that after you defeat the Elite Four, two more areas appear full of Johto Pokemon that you could not get in any other games (besides Pokemon Colosseum).
Team Magma's hideout
To get to Team Magma's hideout, you must first get the Magma Emblem. Then, go to Mt. Pyre. Go through jagged pass until the screen shakes, and an opening will appear. This is where Team Magma's hideout is located. REMEMBER: Do not go to Team Aqua's hideout first.
Mirage Tower
After you get the fourth badge, jump down the rocks (left of Lavaridge). Go to the desert. You will see a sand castle. Go to the top to get a fossil.
Water Institute
The Water Institute is where you received Castform from that building.
Battle Symbol
The easiest place to get a Battle Symbol is in the Battle Pike. Complete it three times and you will see Lucy.
Blue or Red Tent for secret base
Go to Route 110. Go to the Trick Master's house and complete every challenge. This requires Cut and Strength HM. After that, he will say he that needs to travel. He will give you a Red Tent or Blue Tent.
Belue Berry
Go to the Berry Master's House and talk to his wife. Tell her "SUPER HUSTLE".
Cheri Berry
Go to the Berry Master's house and talk to his wife. Tell her "OVERWHELMING DAY".