Overview:

Environment: Ossus was a lush verdant planet full of flamboyant flora and fauna. It was left inhabitable and damaged in 3996 BBY by a shockwave caused by the Cron Cluster, which was later known as the Cron Supernova. This supernova was caused by Exar Kun, who manipulated Aleem Keto into using the Corsair, Naga Sadow's ancient battleship, to detonate the Cron Cluster. The detonation caused the Cron Cluster to explode, and it would radiate Ossus, rendering it uninhabitable. The damage was reversed around 4,000 years after the catastrophe, however, there is no known explanation for this. 

Localization: Ossus was an Outer Rim Planet located within the Auril sector, and more specifically, the Adega System. Ossus had two suns known as Adega Prime and Adega Besh, as well as two moons, Mim and Nerit. 

Great Jedi Library: The Great Jedi Library was located within the planet of Ossus. Originally built By Odan-Urr, and it was intended for the purpose of spreading knowledge to any who seek it. It wasn’t restricted towards the Jedi or any group of people, whoever wished to study at the library was allowed to do so. Regrettably, the library will fall victim to the Cron Supernova, and will be turned into mere ruins, a fraction of what it once was. Though the destruction was devastating, a lot of the knowledge was moved to other planets such as Coruscant. This was all part of numerous contingency plans that were established in case of emergencies. 

Jedi Academy: The Jedi Academy would serve as a sanctuary for the New Jedi Order, and will be established after the destruction of the praxeum on Yavin IV. It was an oddly shaped building, with an odd layout within it. The Academy would be raided by the Sith and the Empire (130 ABY), during the event known as the Massacre of Ossus. Luckily, around half of the Order would not be present during the raid. The Temple would be destroyed shortly after this massacre, in 137 BBY. 

Knossa: Knossa was the primary city of Ossus. It was located in the Eocho Mountains of Ossus, an abundance of mountains located towards the south of Ossus. It served as the host to one of the first crystal caves used by the Jedi Order, home to the Adegan crystals. Knossa served as the center of Jedi culture within Ossus, home to the Praxeum, spaceport, and other important things. 

Occupancy: Ossus would mainly be composed of young Jedi and force users. Though, there were scholars and knowledge seekers who took refuge in the Great Library, devoting their professional lives towards studying the knowledge within them. After the supernova, those who survived became known as the Ysanna, and were a part of the Ysanna Tribes.