The Sea of Sand was once part of the Endless Ocean. It was pushed upwards by tectonic shifts, causing the water to disappear.
Now it is a vast expanse of desert, located near the Glacier Barrens, Birchwood Forest, and New Ninjago City.
During the Serpentine War, the sea was used as a headquarters for the Serpentine army. After the Serpentine were defeated, the Anacondrai were sealed away in the Sea of Sand, the city of Ouroboros was buried beneath the earth, and the Great Devourer was put into its slumber beneath the city.
A few notable locations within the Sea of Sand are The Anacondrai Tomb, Ed and Edna's Junkyard, the Lost City of Ouroboros, the Desert Pyramid, Crashcourse Canyon, Torchfire Mountain, and Kryptarium Prison.
A dark being emerges from the Forest of Tranquility to the Sea of Sand. It treks across the desert, traveling to the Elemental Masters Dojo.
A couple miles away, the creature sees the energy shield surrounding the dojo. It growls. "Equinox..." The being says. Inside it's mind, Java speaks. "Well, looks like you aren't getting anywhere with this plan of yours. Can I go now?" "Foolish child. This is but a small stone in my path of conquest." "Really? So what's your next move, tough guy?" "I need a base of operations... A fortress... A barracks."
The being turns and runs toward the outskirts of New Ninjago City.