It seems only fitting to send off with a nod to Planetary Romance....
(EDIT: Sorry, was out of town on business and didn't realize the post scheduled was missing the entry info....)
The Dyson Sphere Astrus and the Observer
The first ship to explore the Dyson Sphere of Astrus was the ISS Intrepid, an Aegis Division cruiser assigned to deep space exploration and research. While cataloging systems in the Far Rim they stumbled across a vast construct, what looked much like a Dyson Sphere of immense age and incredible design. The sphere had been drifting in its own orbit, headed out toward the rim of the galaxy for millions of years. Some dating efforts suggest it had been in transit for close to thirty six million years now.
The interior of the Dyson Sphere contained a vast human-friendly artificial ecosystem, which for all intents and purposes was its own lush world environment. The circumference of the interior contained roughly as much surface territory as thousands of Earths. At the center of the Sphere was what appeared to be a cool white dwarf star, moving under an unknown power source. They knew this because it periodically adjusted trajectory...
Astrus became an instant sensation when it was discovered that the interior world contained dozens of sentient races, many of which were genetically identifiable to current existing species, although with enough distinct differences to suggest some form of parallel evolution. The first explorers discovered evidence of colonies set up by the ancients of the Coreward Expanse, and began looking for evidence that they might still exist in Astrus in some form. What they found was more perplexing than anything; evidence of dozens of other civilizations, most never before seen, that had previously encountered the sphere and then just...disappeared.
It was the discovery of the Observer, an enigmatic figure that appeared to be a force-field projection by impressive working ancient technology that took the first explorers by surprise. In the decades of initial exploration the mystery of the indigenous races, the disappearance of prior explorers and the question of who built the sphere and why were of preeminent concern. But when the Observer manifested and changed those explorers, many questions began to be answered.
The observer did not speak; it is believed by some to be an AI construct of the ancient civilization that created the sphere. It demonstrated a shockingly effective mastery of transgenics and nanotechnology (or so it is believed), recreating the researchers into species indigenous to the world, rewriting them at the molecular level and leaving only memories intact. In short order the crew were transported by means of teleportation (fold space discs) across the globe, to their new "natural" habitats...
Since the incident, two more research expeditions have met similar fates. In 2854 a Tetragon Union vessel approached the sphere and attempted to sieze control of the machine's inner workings, but something happened, and the crew disappeared (presumably changed), and their vessel outside was pulled into what appeared to be a black hole which disappeared as suddenly as it manifested.
Today, researchers who attempt to explore Astrus take careful measures to arrive without any technology at all, space-dropping in and going native for as long as possible. It has been determined that the Observer only takes notice when a full expedition with gear and tech arrives. There is a suspicion that for whatever reason Astrus is some sort of ancient "eco-reservation" of long lost alien species. Still others think that the unusual genetic similarity of the aliens on Astrus suggests more sinister purposes. Groups like the Tetragon Union are convinced that the technology of the sphere will make them invincible, if they can just defeat the Observer.
Today, the Federated Commonwealth assigns cruisers to routinely survey and observe Astrus from a distance, and to act against any unauthorized aggressor or incursion from threats such as the Tetragon Union, while providing scheduled pick up and drop-off of Academy scientists and Aegis investigators who "go native" to explore the artificial world.