Xaohuac

The jungle hills of Metzono are expansive. The moist earth rises and falls in hills and valleys. The tree coverage stays the same, but the life begins to teem further down the hills until one reaches the Xuahoac and Xaohuac. The earth falls down to small cliffs along a narrow passage of water before small cliffs again and rising to the jungles of Hezhz. The land here is locally named Xuahoac. The strait is named Xaohuac. 
For eras, Xuahoac received praise from naturalists in Kattumalu and other places of learning as having the most diverse life forms. Indeed, species of lizards, birds, alligators, snakes, monkeys, and other creatures existed here. Even some dinosaurs have been seen prowling the deep jungles in shrouded ravines where sunlight never reaches the depths that time has forgotten.
And so it had been until the naturalists, with help of magic, were able to explore the waters of Xaohuac. It was well known the Sea of Reefs got its name from the great reefs that grow in clusters all the way from Xaohuac to Trimton to the unknown East. The reefs in Xaohuac were notable for their colors and structural composition. Bright fish swam in and out of the holey reefs, nabbing smaller fish or plants as they went. 
Then, when a naturalist who had heard of the beauty of the reefs felt let down by what he found, decided to get as many waterbreathing potions and supplies and set out at dawn as far down as he could go. He swam with the help of some potions and spells to a shelf. Many had achieved this shelf and peered down into blackness. None had ever gone down for fear of drowning, and the easily acquired fish and flora of the sunny uplands held their attention. The brave naturalist dove down into the inky blackness. 
After a few minutes, he began seeing small lights flick on and off in the near distance. At some length longer he began to feel watched. An overwhelming sense of dread came over him, but he persevered, and was rewarded. To his utter delight after several more minutes of swimming the blackness faded, giving way to a soft green and purple glow. Like a bird descending from the clouds, he popped out of the blackness into a completely unknown realm.
He saw an expanse. larger than he had ever seen save the sky. A limitless darkness fell below him, far, far away. In between him and that darkness, though, rocky crags fell this way and that, holding many structures on and in them. There were large structures of porous stone or reef or mushroom spiraling this way and that way. A few quite common looking mushrooms spread out like a soft bed, their undersides fanning with some of the soft green light. What can only be described as underwater trees swayed in currents. Their leaves were a pale white and curled at the edges towards themselves. Floating barbed stones that resembled gargantuan clamshells swayed in unison, even against the undersea trees' swaying.
There were fish, or what can be defined as underwater creatures, darting this way and that with fins or tentacles or rope-like appendages that "grabbed" the water to use for locomotion. Some of these stopped immediately upon noticing him. Some had teeth the size of his head, and others stony mouths for grinding on the rocks and polyps. Some flat-bellied sharks swam up in a side-to-side motion to him, touching them with long thin tongues. They snorted and swam away quicker than he could see. A few other curious creatures bobbed up to him, producing bony arms to prod him. Satisfied with this, they surrounded him and with bubbles pushed him further down.
The further down he went, the more surreal the scenery. Yes the darkness was still below him and the spires and walls of rock were around him, but underneath this further plains of stone and grass swayed in currents. Small house-like structures sat with lit windows. A merfolk glanced out and shut the window. The creatures still surrounded him and pushed him further down. 
This next plateau revealed lava floes, burning and hot. The water around him bubbled at the heat. Not much lived here except a few oversized undersea salamanders that swam in the lava. Red bushes creaked and cracked in the heat. The perpetual water sloshing sounds ceased further down.
Here, the blackness and weight of the water suppressed him. Whereas before he had miles of structures surrounding him and easy to grab, now he had nothing. A loud roar shook the water. His eyes almost popped out of his head at the pressure that roar created. Off in the distance he saw, swimming towards him with feverish intensity, a large tube like thing with fins jutting off the sides, moving gracefully in the water. It had pale skin that shimmered in his light. As it came within several yards its front tapered end opened into rows of infinite teeth and a sickeningly pink mouth and black hole to its stomachs. 
Just as it came within several feet, it used one of its fins to cover the single large eye on the front. The light stopped it. He knew he had to swim upwards and fast. He downed a potion of haste and swam with his enhanced speed and webbed hands back up and up and up until he reached the surface. He went on to go on several expeditions and wrote many books on the vast undersea.

Geography

Great reefs on the top layer. Glowing flora and rocky crags comprise the second layer. The third is lava floes. The fourth layer is the watery void where dwell some of the most horrific and dangerous creatures.

Fauna & Flora

Glowing rocks and mushrooms, grasses and trees that sway in the currents. Red bushes in the third layer.
Merfolk are the most sophisticated creatures living here, complete with a government and societal standards and customs. 
Fish of all kinds, those known and those unknown, live in harmony or fear.

Natural Resources

All manner of gems and geodes can be found in the depths. Silver and gold veins also run along the inner caves. An abundance of fish can be found here, and large, edible creatures are easily captured.

Tourism

Tourists love the reefs teeming with cute fish and wildlife. Every now and then, a tourist falls in, but the dolphincrabs hoist them back up to the surface.

Type

Strait

Location under

Metzono