The Obsidian Sanctum is a raid whose entrance is located in Dragonblight in the World of Warcraft game. The minimum level for this dungeon is 80. The instance was released in the Wrath of the Lich King expansion. The raid contains 2 bosses. The end boss of The Obsidian Sanctum is Sartharion.
There are three twilight dragons, each at various points in the room. THe drakes are named Vesperson, Shadron and Tenebron. If you are soloing this raid at a higher level, you don't really need to go after these dragons as there's nothing to be gained. You should just go for Sartharion and get the mount that drops on either 10 or 25. Back in the day when it was the highest level, it was possible to clear the place with 25 mages, no healers.
There does not seem to be any point any more doing this raid with the twilight dragons dead. All you need to do now, at a high level is to go in, nuke it quickly, get the loot and run. The Lava doesn't hurt any more and you can quite easily swim in there without any damage. The minute you hit the both, all the trash and the twilight dragons will come and attack you. Once Sartharion is dead, the other drakes will not disappear and you will have to get out of the raid or kill them. There are two drakes to be had, one at 10 and the other at 25. There is no heroic level, only normal.