The island: (adventure seed)

From the prow of your ship you see the island comes into view.
At first it is nothing but a glint on the horizon, then a shining sphere.. a glare in the sun, rainbows, refracted and distorted views of the horizon beyond.

• The island covers approx 93 miles (the surface area of a 6 mile per side hexagon):
• The  island is conical moving from pure white beach to a 500 foot peak at it's tallest point.
• The island is covered  in heavy, jungle like vegetation.
• Birds can be seen flitting about the trees.
• It is encased in a sphere of the  purest glass.
• The  sphere is half full of water.
• The craggy pointed bottom of the island can be clearly seen through the  glass.
• Mid way up the  underwater section of the island several cave entrances can be seen. Holes dark against grey grey of the islands base.
• The underwater portion of the island is encrusted with corals and plants.
• There are no debris or any silt at the bottom of the sphere.
• The water is a deep blue green, there are fish visible in the water.
• The sphere hovers 70 feet above the rolling ocean.
• The sphere is massive, slowly  turning on its vertical axis. 
• The turning of the  sphere creates a circular counter clockwise current in the sphere.
• The  only entrance in or out of the sphere is a five foot hole at it's very  top. 
• The  top of the  sphere is  100 feet above the tallest point on the island. 
• The bottom of the sphere is 50 feet from the lowest crag of the islands underwater section.
• The inside of the  sphere is often coated with  condensation.
• It is incredibly warm and humid in the sphere.
• On a warm day it can storm in the  sphere, but rarely thunderstorm.
• During exterior storm the slowly turning but massive sphere builds up incredible static charges.
• On cold nights the sphere generates a plume of fog, the  whole interior becomes a cloud.

Questions:

The obvious one,  how the hell did this end up in the middle of the  ocean?

Why is it here?

Does anyone live inside of the sphere?

How old is it?

Can that static electricity be of some use to someone?

Are there any strange items, creatures, or commodities that can only be found in the sphere?

Why is this thing not on the captain's charts. It's HUGE.
How can we get in there? If we do how do we get out?

Thanks for reading

-Mark.