The Cave to Another World is an optional dungeon that can be accessed after finishing the main game. You’ll need four Mysterious Fragments to enter it. The respective pillar is at the Shrine of Mysteries.
Finding the first fragment
You’ll get the first fragment once you beat the main game. After you defeat Orgodemir, your party travels to every city to be greeted by different NPCs. When you’re at Estard, enter the well on the east side and pick the Mysterious Fragment in there.
Keep going with the cutscenes and save when the game asks you. Reset the game and you’ll be able to continue playing from before the final battle, but you’ll have the Mysterious Fragment in your inventory.
Note: if you don’t get the fragment at this point, you’ll need to repeat the final battle and do the cutscene again to get to the well.
Finding the second fragment
The second fragment is given to you by King Maximo after you gather 85 Mini Medals for him. If you haven’t visited King Maximo’s Mansion yet, just Zoom to Wetlock and fly northwest from there.
When you have the 85 Mini Medals, talk to King Maximo and collect every tier of rewards until he gives you the Mysterious Fragment. There are 118 Mini Medals in the game, so even if you miss many of them, it won’t be difficult to have 85 by the end of the story.
Note: in the original PSX version, you’ll need 100 medals instead of 85
Finding the third fragment
The next fragment is in the Sunken Citadel. To get there, Zoom to Wetlock again but get on your ship this time. Sail to the southwest and enter the shining whirlpool near the coast.
Walk straight north and interact with the pillar to show a secret staircase. Go down there and follow the path north until you reach the next stairs.
Walk on the tiles over the water and get to the third room. From here just follow a linear path through three more rooms until you reach the throne of Gracos V.
If you didn’t beat Gracos V before, you’ll have to fight him now. At this point of the story, you’ll be extremely over leveled compared to him, so he’ll probably die in a couple of turns.
After defeating him, he’ll give you the third Mysterious Fragment. You can also open the other chest to get a Demon Spear.
Finding the fourth fragment
To get the last piece, you’ll have to revisit the Coral Cave of the past. If you don’t remember how to get there, Zoom to the Divine Shrine, get to the north portal and interact with the mysterious pillar.
Follow the same path you had to follow the last time you visited the cave. Once you reach the room with several marble arches, talk to the ghosts in there. The maid ghost will give you the last Mysterious Fragment.
Restoring the Mysterious Pillar
Now that you have all the Mysterious Fragments, Zoom to the Divine Shrine. Search the corners of the main room and go down those stairs. Open the gates with your Ultimate Key and you’ll find the Mysterious Pillar.
Place all four pieces on the Mysterious Pillar and you’ll be teleported to the Cave to Another World. This bonus dungeon will have some of the harder fights up until this point, and a secret boss battle at the end!
