Endless Islands are a part of Atlantis where you can stock up on resources and treasures. They are called "Endless" for a reason: after exploring one island, you can move on to a new one right away!
The portal leading to the Endless Islands is on the right side of the camp. It appears after completing the Growling Grotto.
Endless Islands are rich in unique minerals (Mi'thril Ore, Silver, Gold, etc.) which can't be found on any other locations. To find the needed resource, open the resource menu in the lower left corner and tap the question mark near the item. The hint will direct you to the mineral deposit. Cut out all resources on the island and get awesome gifts!
You'll encounter Protective Statues guarding Atlantean treasures. Make an offering to the statue to unlock the treasure chests. Apart from coins and and useful resources, you can also get Opals and rare artifacts for collections.
Watch out! The predator can block your way. To neutralize the predator, tap it and keep pressing the button till the bar is full. The predator will fall asleep and you can get some extra bonuses by tapping it one more time.