A Beacon of Glowing Shadows

The captain of the ship was fortuitous, quick-witted, and skilled. He also had terrible luck.
That was what got him and his crew stuck in the biggest storm this side of the century's turn. And the crew - though tenacious, quick, and strong - found their efforts to be no match for the winds and the rain. The great many sails had been either folded or reduced to rags, and their ship was in serious danger of capsizing - or being struck by lightning. Whichever one came first, or was more likely - you do the math.
What's worse - they were lost in the storm. It wasn't that wide across, but it would be disastrous if they ended up sailing out the direction they'd come - or worse, circling around in the chaos until they inevitably perished.
So much for being the first ship to cross the stormspan, the captain found himself thinking, even as he was shouting orders and desperately trying to get the ship's course back under control. But he had no idea where to go. Which wasn't entirely his fault; he hadn't expected their charter to fall overboard in the chaos - the man was supposed to be sheltering below. But no - he wanted to watch the clouds. Or navigate. Or something. (You'll have to forgive the captain - he lived at the early period of sail-cloud exploration, the time when sailors weren't exactly navigators).
That was when the light flickered on.
A great golden glow, shining in the distance like the sun. The beam of light reached everyone on the ship. They all paused briefly, and a gust of wind nearly tipped them over. And so, with nothing better to do, the captain called for them to steer the ship towards the light.

No one knows exactly what happened to the crew of the Sunsailer. A few sailors obviously survived the storm, or we would not have found their journals. They wrote about the ordeal of cutting through the tempest, and the burning hope inside that kept them fighting to reach that light. From there, their entries described a tall, circular building made of pale wood - one you would recognize as a lighthouse, but what they called a beacon. After recuperating from their ordeal (the lighthouse was located in a miraculously circular clearijng of the storm, so they stopped there to rest), they said they were going to send men to enter the building and thank their rescuers.
Naturally, those men were never seen again. And, three months later, when the captain's brother followed him into the storm (apparently navigating the stormspan had been a dream of theirs), he, too, found the lighthouse - and the corpse of the Sunsailer, devoid of crew members, but still retaining the logbooks. They left the lighthouse alone. And for whatever reason, they made it through.
No one knows what the mystery of the lighthouse is. It is there, guiding crews through the terrible storm. Some who enter vanish. Others return in excellent health, faces practically radiating light and with a solid streak of luck trailing them for the next few weeks. So what's the deal? No one really knows. And it's up to the crew whether they want to brave the doors of the lighthouse. Some crew members find themselves drawn to the house, others repelled. Boons or curses await those who enter - but why the deviation? Why the unpredictability?
It's safe to say that no one really knows.

The Truth

The return of the spirits happened slowly. But it happened. (I promise, I'll get ot the spirits soon). And with their return, both the good and the bd spirits found themselves wanting to find a way to interact with the Skydwellers.
The lighthouse proved to be their first step. It was molded by the spirits of spring, built somewhat untraditionally, but familiar enough to serve the purpose - the help the sailors on their journey through the stormspan. It would provide a waystop - a place to restock, refresh, and recenter the ship's course.
That was when the dark spirits, as alwasy, messed things up. I'll spare you the details of the struggle between the two groups - and the two caravans who found themselves drifitng into a storm, luring in by a lighthouse, and then killed by pneumonia, of all things. It was a magic pneumonia. But still. The spring spirits quickly recognized that they were at a disadvantage - so they struck a deal. One day for them to have control of the lighthouse. Two days for the dark spirits to have control. It pained them to see the sailors they were so eager to bless fall prey to their adversaries. But they had struck a deal. One day of light - a day for boons, good luck charms, blessings. Two days of darkness - death, misfortune, conflict. A three-day cycle of good and evil, repeating endlessly in one lighthouse.
As of yet, the Skydwellers have not figured out the truth of the lighthouse. Most avoid the stormspan entirely. But it is a predictive cycle, and I am confident that they will one day find a way to master the stormspan - lighthouse included.
For now, they'll have to settle for losing one in five ships to the strange winds that drag sailors into the stormspan - to a false light and a dark curse. But such is the way of the spirits, is it not?

The creation of airships changed everything for the Skydwellers. Previously, supply expeditions into the Outer Realm weren't exactly expensive - but they weren't cheap either. The cost of training pack animals or hiring supply carriers was...formidable. At least the charter guies were free - the charters had already been paid for by the government. Still, large businesses had previously been the only ones able to afford the trips - and although they were met with enough success that the supply and demand of the more uncommon goods remained roughly in balance, the invention of ships made carrying cargo all the more easy, and suddenly the supply expeditions were open to all.
 
The effect was achieved using a special device - the cloud-shearers. The specifics are relatively unknown by the general public, but they were created while studying the effect of tree roots on undercloud caverns and the digging appendages of burrowing animals. And they were a huge success - though their production was limited, especially at first. Still, the most immediate effect was the new reliability of trade routes opening up to businesses that relied on commercial expediitons - that is to say, over 70% of the current corporations. You can imagine the effect - not only the finalizing of trade routes, but the sudden race for supply lines (and the emergence of pirates, but that's a story for another day).
Of course, if those dang scientists had just been able to find a way to domesticate any one of the valuable animals or plants so necessary to modern Skydweller life, the whole ordeal of creating ships could have been avoided. But apparently creating an entirely new science - that of cloudcarving - was easier than figuring out how to relocate the stubborn seeds of the Outer Realm plants (and if you're wondering why so many of the Skydweller's most valuable resources are so far away from their settlements, ask yourself if you'd like to build a home at the bottom of a river for its access to freshwater).