Deepsea Ruins is the fifth level of Soda Jungle in New Super Mario Bros. U, located in the haunted sub-area of Soda Jungle. It takes place in a presumably steaming lake. This level uses the volcano underground music theme from New Super Mario Bros. Wii (which would later be used in Rising Tides of Lava) despite its environment being a haunted forest until the player reaches one of the level's exits, whereupon the music becomes the forest theme from New Super Mario Bros. Wii.
Completing the course normally makes a path that leads back to the first point after Which-Way Labyrinth, but completing the level with its secret exit reveals the true path through Soda Jungle, leading to Seesaw Bridge and Wiggler Stampede being unlocked.
The level begins above the water, with Stone-Eyes acting as prominent platforms, similar to Stone-Eye Zone. Fish Bones are encountered in the water, and Circling Boo Buddies are also found. There is a Warp Pipe at the end of the area, leading to the next area. The second area takes place in a dark underwater cave. Jellybeams and Fish Bones are found at the beginning of the area, as well as a ? Block containing a power-up. Stone-Eyes are found, acting as walls, along with Circling Boo Buddies. A Red Ring is also found. Some more Fish Bones are found, along with Stone-Eyes that move forwards when approached. A Jellybeam follows, as well as a Warp Pipe leading to the next area. The Checkpoint Flag is found, as well as a Bulber and Circling Boo Buddies. The area continues vertically, where more Stone-Eyes, Bulbers, Fish Bones, and Circling Boo Buddies are encountered. A ? Block containing a Starman is found in between two Stone-Eyes. A group of Stone-Eyes begin to fall when approached, along with more Bulbers. A Warp Pipe at the top of the area leads to the Goal Pole area, with Stone-Eyes acting as platforms.
- Star Coin 1: The first Star Coin is between two Stone-Eyes.
- Star Coin 2: The second Star Coin is within a group of Circling Boo Buddies.
- Star Coin 3: The third Star Coin is to the right of the end of the underwater section. To the right is the Warp Pipe that leads to the actual goal (which is marked as a secret exit).
Unlike most secret exits in the game, this course's secret exit is required to continue through Soda Jungle, like Painted Swampland. A Warp Pipe leading to the secret exit is immediately to the right of the third Star Coin.