For a planet that has, supposedly, been closely observed since long before any living creature touched it, Saturn holds an awful lot of mysteries.

The Birds

Many visitors, and even some inhabitants, are under the impression that Saturn is exclusively urban, with cloud-cities that may as well be floating in an empty stretch of space- but the expansive atmosphere is neither featureless nor uninhabited.

A dispersed and mobile society of bird-like machines live in the clouds (mostly the water-ice ones, several hundred kilometers below the more traditionally inhabited "top deck"), inhabiting descended wreckage or nests they build themselves, but often flying for weeks at a time. Physically, they resemble Earthly pteradons more than birds, built with a combination of large-scale robotics and flexible metallic micromachinery. They are, for the most part, fusion-powered supersonic fliers.

They have their own culture and societies, and describing these in brief is made even harder by the Birds being seemingly deliberately obscure. They play games and form political structures, and are often seen flying in thunderstorms or alongside aircraft when they visit the upper atmosphere. They're reasonably well-known and a common sight, but nobody (except perhaps themselves) are sure where they came from: They were never spotted during the interplanetary period, no large manufacture or immigration of the Birds was recorded at any point, and the answers they give when asked are contradictory and vague.

One popular theory is that the Birds are mostly Terragen uploads deliberately cultivating a cryptid reputation. One Bird, when asked why they're here, answered that "such a wild place ought to have monsters".

Still, some of their characteristics don't quite line up with a Terragen origin. A few birds have gone to cities for medical treatment, and their engineering is distinctly alien- specifically, it resembles ancient Sivkan "silverskin" robotics, machines that have been historical relics for thousands of years. When asked how they got to Saturn, most of the Birds say "they flew", but this may be humor.

Their own mysteries aside, the Birds are keenly observant of happenings in Saturn's lower atmosphere, and discovered many of the world's deeper secrets.

The Temple Under 70°N/42°E

In the year 12082ET the transport aircraft "Fouriest" lost power and backups, and went down on its way to the north pole research station.

Normally, this is very fatal. Saturn doesn't even have ground to crash into; at the time, most lost vessels would be crushed under increasing pressure and either find buoyant equilibrium somewhere in the lower atmosphere or continue in fragments to the rocky core.

This plane, supposedly, landed.

The crew of three made repairs and returned to their course, but not before exploring the structure they found nearly a hundred kilometers below zero. It was, by all accounts, a large stone building suspended in the atmosphere by unknown means, with several uncovered platforms surrounding a central tower. The stone itself resembled Martian basalt, and was in many places shaped into striated pillars somewhat resembling those of ancient Greek temples.

Several large (15m tall) doors connected the outer platforms to the tower, but the crew was unable to open them. They recorded their exploration of the outer walkways, though, which contained several notable structures- Many hexagonal daises carved with knotlike patterns, two stone orreries, and a series of rings seemingly aligned with Saturn's axis.

How the structure got there, and where it went later, are entirely unknown. Their air supply eventually forced the three to return to their craft and leave, and the stone structure was never found again. Two of the crew quickly moved on after the encounter, but the third pilot, M. Vidya, remains involved in Saturnian exploration.

There's little else to say about the lost temple itself, but three years ago, M. Vidya underwent emulator uploading. She discovered inconsistencies in her memories consistent with Lakvanku information transfer in biological brains, opening the possibility that their records of the temple are somehow inaccurate or incomplete- and involving the Lakvanku.

Dragon's Disappearance

Since probe observation began from Earth, a thunderstorm called the Dragon Storm reliably lit up Saturn's southern hemisphere at night. Eternal storms are not unusual on gas giants, and the Dragon Storm's appearance at night and disappearance in the day was only slightly out of the ordinary.

The Dragon Storm disappeared for good, though, while the suspended fuel refinery that eventually became Sigillaria was under construction. Observation of the storm wasn't continuous at this time, but satellite footage shows that its sudden midnight end came within, at most, two hours of the platform's reactor powering on for the first time.

Theories abound, from "extremely unlikely coincidence" to the dragon storm being the deliberate or accidental influence of an ancient atmospheric probe that was activated by neutrino emissions from the first reactor to run in its immediate proximity.

Fractal Structures

On at least eleven occasions, massive solid structures were observed in Saturn's lower atmosphere by photography or radar. Each roughly resembled a simplified pyramidal Koch surface, hundreds of kilometers long, with as many as nine of these objects seen at once.

The first time they were detected in the later interplanetary period, they floated well below the crush depth of any aircraft of the time, and were noticed only on radar- the intricately fractal and apparently conductive structures made excellent radar reflectors. Later, they were seen by deep-atmosphere explorers, and found to be of elaborate construction with moving parts and internal structure with apparent floors or layers inside. The fractals moved away when approached, and thorough scans of the planet never found them outside of their rare coincidental appearances.

Their apparent disappearance and reappearance drew comparisons to the long-lost temple under the clouds, but their composition and construction differs dramatically. The most mundane explanation is that the fractals are natural crystalline formations of hydrogen, coreward minerals, or ice; possibly catalyzed by the exotic hydrogen phases in Saturn's metallic layers. Some theorists posit that they may be agglomerations or flocks of airborne Saturnian lifeforms never noticed when they're diffuse, but many find it difficult not to reach for 'ancient alien megastructures'.

Elegies

There is compelling evidence that the entirety of Saturn was destroyed on two separate occasions during the interstellar period. That the planet still exists is troubling, to say the least.

The first so-called elegy was found by the Birds in what appeared to be a wrecked section of Sigillaria floating deep in the atmosphere (although, Sigillaria was never correspondingly damaged). The caches and buffers of several appliances and tools found inside recorded a horrifying disaster that never took place: By some unknown mechanism in the year 12162, Saturn collapsed over the course of several seconds, leaving its cities to fall to the compacted core and killing all inhabitants.

The second elegy was discovered in 12199 in the apparent magnetic noise received by survey satellites, and contained fragmentary transmissions and calls for help during a similar disaster. Partial copies of at least two different minds were found in the data, but were never successfully revived. Some of the contents were verified against still-in-use governmental cryptographic keys, all but ruling out the possibility of forgery.

There is, so far, no explanation for the elegies. After the second was recovered, every city in Saturn made sure their platforms were spaceworthy and capable of escaping the planet's gravity.

...And we haven't even STARTED on the moons!