Dromund Kaas, a jungle planet, was discovered by the Sith quite some time ago, but the location was lost and the planet forgotten in the recesses of history. That is, until the Sith suffered a horrendous defeat some thousand years back, at which point the remnants of the fleet happened upon the forested world. They spent generations building their force back up, which included turning the atmosphere into a nonstop electrical storm (how that helps with launching an attack on a larger entrenched military is somewhat questionable, but let's not sweat the details).
Even with the Sith powerbase expanding, Dromund Kaas remains the center of intrigue, politics, and all that goes along with the above. No doubt there are a large number of future Star Wars: The Old Republic players already thinking about what adventures might take place on the planet's surface, so take a look at the official update, which includes further screenshots, concept art, and a video flythrough of the planet.
