This page details everything you need to know about how and where to find the Mossy Key for the Sunken Treasure Chest, located in the depths of the Koi Pond in Grounded. We’ll cover the appropriate underwater gear that you’ll need and how to stay alive without losing oxygen as you swim for the key.

Where to Find the Mossy Key¶

The Mossy Key is required to open the Sunken Treasure Chest in Grounded, which provides you with a Mega Milk Molar and a BURG.L Chip. Thankfully, the key isn’t too far from the chest, which you’ll find in the cave where the T-Rex toy dwells, leading into the Pond Lab.

The Mossy Key can be found inside a dark tunnel beneath the Pond Lab, which is populated by a number of Diving Bell Spider enemies. This is a good thing in this case, since each time you kill one of these spiders, you’ll recover your oxygen levels to full.

If you don’t get enough oxygen from killing the spiders, you’ll also find a tube with oxygen bubbles coming out of it in the same area where you find the Mossy Key. You can stay above this tube to replenish your oxygen for as long as you like, before you make the journey back to the main chamber where the Pond Lab, T-Rex, and Sunken Treasure Chest is located.

Before you make the journey through the depths of the pond, we highly recommend that you craft and equip the Bubble Helmet, Fin Flops+, Slime Torch or Slime Lantern+, and a Bone Dagger or Bone Trident. This will give you the best chances of success since you’ll be able to stay underwater without oxygen for longer with the helmet, you can swim faster with the footwear, you can actually see where you’re going with one of the light sources, and you can kill the spiders quickly with the dagger or trident.

To see exactly where you need to go from the main chamber to find the Mossy Key, see the video below.

How to Unlock the Sunken Treasure Chest¶

Once you’ve got the Mossy Key, all you need to do is return to the main chamber to open the Sunken Treasure Chest, loot the BURG.L Chip and Mega Milk Molar. You’ll need to do this as quickly as possible from the point where you found the key, then swim back to the oxygen tube near to where the T-Rex is.