Massive sea at the north. I have come across no chests, or caves whilst exploring out there. Is there any underwater items like the glass helmet in Oblivion?

I've found a fair amount in various dungeons, but nothing in the exterior areas. I haven't done much in the ocean, but my wife has done some extensive swimming down rivers and hasn't found anything of interest under water.

Why have a Waterbreathing skill if theres nothing underwater?

Why have waterbreathing potions if theres nothing underwater?

Probably something they wanted but didn't finish?

I haven't found anything underwater besides a few chests in dungeons. And I didn't need to hold my breath for longer then 3 seconds to get to them.

i've stumbled upon a couple of underwater "dungeons" (mainly sunken ships) but have yet to properly explore them

There is a graveyard of ships underwater.
The Daedric Prince quest.
A shrine of Talos out in the ocean with a hidden treasure chest if you do a certain quest in the College of Winterhold.
And I'm sure there are more to be found.

There are many underwater chests. They're pretty easy to find if you spend a significant portion of your gametime looking for barnacles and clams.

Like I do.

:sadvaultboy:

I did do a little exploring up north but got scared, it felt like a kraken was going to leap out swallowing me whole at any moment. Aside from a ship wreck, stone and outpost, there doesn't seem to be a lot up there or underwater though. probally more calms then anywhere else, alot of ore points, and a altar a little to the south...oh and plently of death on land with every snow creature going. but underwater I never even saw a snow slaughterfish.