Shadow Tundra is the 4th chapter in Sword of the Sea. This guide contains all collectible locations and everything you need for trophies/achievements.
Collectibles Overview:
Shadow Tundra Collectibles
Stele #11: Fire Elemental – After the scene dropping through the ice, the stele is directly in your path.
Stele #12: Ghost Warrior – At the third statue (you can’t go far off the correct path in this tundra area, keep moving in the direction the statues are looking) it is on the ground in the hand of the buried statue.
Secret Shell #23 – At the fifth statue (the second after the stele) climb up the ledges on its back, then its arm to reach the sword where the shell is at the tip.
Stele #13: The Ghost Warriors Undoing – When you reach the open area with the giant statue in the middle, go down the path to the right to a mural with the stele in front.
Water Point #1 – On top of the statue’s hand, after using the kelp inside to reach its eye socket.
Rideable Animal: Humpback Whale – After restoring the water by activating the point on the statue’s hand, a bunch of fish will appear in the area. A few of them are Humpback Whales. Jump on one using the kelp that has appeared in the area to receive the trophy/achievement Humpback Rider 
after you jump off.
Secret Shell #24 – After activating the chain linked to the statue’s hand, ride the chain up to it and the shell is at the tip of its sword.
Secret Shell #25 – When you reach the ice slide area, stick to the right where the group of 6 statues is located to find a small cave between the first and second on the right where the shell is located.
Secret Shell #26 – After the tube in the hall with the pillars, the shell is located on the right between the third and fourth last pillar.
Secret Shell #27 – In the next area you have the ability to use boosts by picking up wisps from the lit pillars. Grab a few (you can store up to 5 at once) then go near the top of the area and look back toward the entrance left of the shark statue where there is a jellyfish jump leading to some far away platforms. Boost and use the jellyfish jump to reach the closer platform with the chest, then boost and jump to the two near the entrance where you can find the shell at the end of the farther one. You can also use the jellyfish jump but aim to the right of the platforms to earn the trophy/achievement Long Distance Jumper .
Water Point #2 – Use the jellyfish jump left of the previous one to reach the far doorway. Enter the area and follow the path of bones to reach the water point, awarding Cleanse the Cleanse the Frozen Tundra .
Secret Shell #28 – The shell is inside the skull directly above the water point.
Rideable Animal: Elasmosaur – After restoring the water by activating the point in the skull, a bunch of fish will appear in the area. A few of them are Elasmosaurs. Jump on one using the kelp that has appeared in the area to receive the trophy/achievement Elasmosaur Rider after you jump off.
Stele #14: Forgotten Eras – At the back of the same area on the lowest level, under some stone snake heads.
Horned Frog – After interacting with the first gold bell to reach the giant open area, go toward the back to find a ramp leading to the tallest platform in the middle of the area. Boost and charge jump to reach it to find the frog on a stack of rocks, awarding the trophy/achievement Horned Frog .
Stele #15: The Dual of the Sea – On the left side of the central pit near the tall platform with the three pillars, there is a cave behind it where you can find the stele.
Stele #16: The Great Shark – On the left side of the area on the platform with the bell, go around the back where the stele is sitting in the chest hole of a shark statue.
Secret Shell #29 – Jump around the left arm of the shark statue to find the shell behind it on a ledge.
Secret Shell #30 – From where you entered the area stick to the right wall through the round rock structure, then go into the rocks on the left where the shell is secret.
Secret Shell #31 – From the same location look back toward the round rock structure where there is a snow ramp to the left. Boost and jump off the ramp on top of the rock structure where you can find the shell.
Trick Attack Area #3 – On the far right side of the area past the golden bell you can find the time attack area. Beat the high score of 10,000.
Secret Shell #32 – Near the exit of the area to the right of where the vendor is sitting there is a small corridor in the ice with the shell at the back, awarding Shadow Tundra Shell Collector .
NEXT: Frozen Drifts
Helen says
The bit of the ice slide region where the shell is in a cave on the right is also the bit with the snake and shark frozen under the floor. Neither moves. Te cave opening is directly along the line between them.
DM says
Shell 23 has been moved, it’s no longer at the tip of the sword but just at the shoulder, before you climb the arm to get the to the end of the sword. You still get a hidden burst of gems if you climb the sword though!