This place is accessed after obtaining the Amaranth Badge. It can be accessed by going to the middle-east of Tourmaline Desert. There is no requirement to enter the cave.
If the player is traveling with Taka, he shares some insight on the history of this cave, mentioning how it was once home to his ancestors. As the player and Taka progress through the cave, he remembers more and more about going to the cave as a child with his father, Solaris.
There are many sinkholes in the cave, some of them will take you to new areas when you enter them. Other sinkholes will lead you back to the entrance of the cave. To save time, save the game and enter one of the sinkholes. If it leads you back to the entrance, restart the game to go back where you were. There is only one correct path of sinkholes that leads to one of the statues.
The path towards the statues are as follows:
Left Statue: Left hole -> Ladder northwest -> Middle left hole(Left of broken pot) -> Ladder north -> Middle topmost hole -> Ladder east -> Go east to a cave
Right Statue: Right hole -> Ladder northeast -> Middle topmost hole -> Ladder west
There is only one ladder each room
Places of Interest
Swimming In The Sand
At the entrance, go into one of the many sinkholes to find one that leads to a path of stairs being blocked off. In order to activate the stairs, you’ll need to activate two switches above it, which you need to go through many other sinkholes to even reach one of them. After activating both of the switches, go back to the middle hole on the entrance to find the stairs activated. Go up into a cave, which has many Garchomp statues that will chase and battle the player when near them. If you brought Taka with you, he explains how the Garchomp statues were set up as a trail by his ancestors to guard the inner ruins.
After escaping through the exit, the player will enter an entirely new area, the Sugiline Ruins, the ruins of Taka's ancestors' long-gone settlement. Debris and many hidden items are scattered about the area. At the back, the player will find TM71 (Stone Edge), a healing star, as well as an Arceus statue. Interacting with this statue will open up sinkholes that will lead you to the bottom floor of the ruins. Here, there are more items to pick up, such as a Medichamite.
An Offering for a Sand Shark
There are many basins scattered about the area. Fill one with PokeSnax and leave by going into a sinkhole. Go back and return to the same spot to find a Gible. Gible will swim away if you approach it anywhere on its side, so you need to go to a sinkhole that has a basin directly under it to appear behind Gible and battle it. The Gible will always know Outrage and Iron Head as its egg moves.
Sugiline Cave is named after the crystal Sugilite.
Taka and Solaris came here when they were younger. It's also where Solaris got his Garchomp (which was a Gible at the time). Solaris tried to catch a Gible for Taka, but Taka didn't want one, which Solaris said Taka ruined the whole trip when they left.