Visari Palace, also known as the Imperial Palace, was Autarch Scolar Visari's home, and also the most important and well-defended place on Helghan. This is the final mission in Killzone 2 and takes about an hour to finish, excluding any possible deaths.
The beginning of the mission starts with the deployment of Sev, Natko, and Rico on the Lazar Highway, a couple of miles from Visari Palace. You are required to take out four control towers that power and control the massive Arc Battery, which is keeping the ISA troops from reaching the ground from their Cruisers.
After doing so, an ISA Cruiser destroys the battery with its laser. After this, you must fight dozens of Helghast troops in a 300-meter gauntlet, which is basically Visari's courtyard. After doing so, you get to enter Visari's Palace proper. During this stage you are confronted by Colonel Radec leading to the final battle. It is frustratingly hard on the highest difficulty, Elite, but the Trooper and Soldier difficulties will keep it moderately challenging.
After the final face-off with Radec, you are treated to the final cutscene of the game with Scolar Visari, and one of his amazing speeches. This speech takes place in the Autarch's Sanctum, which was supposed to be Visari's sanctuary in case the ISA did ever get past Pyrrhus's defenses and break into the Palace.
Rico then shoots him after getting angered by his speech against direct orders, and in doing so he ruins the main goal of the ISA invasion: to capture Visari alive. It leads to the power struggle in Killzone 3 that Visari warns would take place if he were to die.