Tap the Sunken Temple. You'll know that it's available for opening Treasure Chests when you see the chest floating above the Temple.

 

Choose from:

• Temple Dive is the more common treasure but also gives useful expansion parts and other rare items.
• Secret Chamber has more valuable prizes, including Gems.
• Crystal Cavern gives you the best chance to get Gems.
  
  

Temple Dive

Every eight hours, you'll be able to open a Treasure Chest for Free! After selecting, you will be presented with locked Chests to select from. Pick one and see what you’ve won!

 

Note: After you have used your first Free Dive, you will be charged Coins. The price will increase incrementally with each new dive you make.

 

Succeeding dives will always charge you where you left off during the last dive that day. The coin price will refresh every 24 hours.

 

If you want to see what the possible remaining prizes are, tap on the Prizes? button in the lower right corner of the screen.

 

After spending coins, you'll reach a point where you will need to use Gems to continuing searching the current selection of chests. The Gem cost will also increase with each dive.

 

Or you can wait eight hours and come back when it's free to do the Temple Dive again.


Secret Chamber

 
The Secret Chamber opens by using a Treasure Key, which also allows you to open a chest. Each additional chest requires a Treasure Key to open it.



To obtain Treasure keys, you can:

• craft them at the Smithy using Iron Ore, Silver Ore, and Gold Bars. Gold Bars are also made at the Smithy. Iron Ore and Silver Ore comes from the Smugglers' Cave.
• open chests when you expand to new areas on the island.
• visit landmarks.
• open chests in the Temple Dive.
• win them as rewards in the Weekly Resort Rating and Leaderboard competition.
• or buy them for Gems!
  

 

Gems are very valuable and the Crystal Cavern offers you the biggest chance to get them in the game. You have a choice of 5 Sunken Chests to open.

And other than Gems, you can win all these other prizes: