Aegon first set foot on Westeros in the area of King's Landing at the start of his War of Conquest. On the highest of the three hills of the area, he built his first fort of earth and wood. After the completion of the Conquest, Aegon ordered the construction of a permanent royal castle on the hill. The construction was completed during the reign of Maegor I, who killed all those who worked on the castle to preserve its secrets.
The Red Keep is made of pale red stone. It has seven massive drum-towers with iron ramparts. Massive curtain walls surround the keep, with nests and crenelations for archers. Thick stone parapets, some four feet high, protect the outer edge of the wall ramparts. The heads of traitor's are traditionally placed on iron spikes between the crenels at the gatehouse. The walls have great bronze gates and portcullises, with narrow postern doors nearby. The immense barbican has a cobbled square in front of it. Behind the walls are many small inner yards. The courtyards are filled with stray cats.
Inside, the Keep has several gathering halls, including the Great Hall, which can seat 1,000, and the Queen's Ballroom, which can seat about 100. Relics of the Targaryens, such as dusty suits of black armor with dragon scales cresting their helms, sit in hallways. Doors are made of oak banded with black iron. Rushes are used on the floors as the weather cools. Overall, the Keep is not particularly large, being smaller than Winterfell.
Maegor's Holdfast is a massive square fortress inside the heart of the Red Keep behind walls twelve feet thick and a dry moat lined with iron spikes. It is a castle-within-a-castle. The royal apartments are in Maegor's Holdfast. The king's bedchamber has twin hearths. The Holdfast contains the Queen's Ballroom, a hall only half as big as the Small Hall in the Tower of the Hand.
Tower of the Hand
The Tower of the Hand is the chambers of the Hand of the King. Its Small Hall is a long room with a high vaulted ceiling and bench space for two hundred. The private audience chamber is not as large as the king's, but has Myrish rugs, wall hangings, and a golden-tinted round window that give it a sense of intimacy. The Tower also has a solar, and a garderobe.
White Sword Tower
White Sword Tower is the chambers of the Kingsguard. It is a slender structure of four stories built into an angle of the castle wall overlooking the bay. A round white room, known as the Round Room, has whitewashed stone walls hung with white woolen tapestries, forms the first floor. The undercroft holds arms and armor, the second and third floors the small spare sleeping cells of the six brothers of the Kingsguard, and the topmost floor is given over to the Lord Commander's apartments. His rooms are spare as well, but spacious, and they stand above the outer walls.
The Great Hall is the throne room of the king. The Iron Throne sits on a raised iron dais with high and narrow steps. A long carpet stretches from the throne to the Hall's great oak-and-bronze doors. The Hall itself is cavernous, and can sit 1,000 people. It is oriented north to south, with high, narrow windows on the eastern and western walls. Skulls of the Tragaryen dragons once adorned the walls, but Robert Baratheon had them replaced with tapestries at the beginning of his reign.
The dungeon of the Red Keep has four levels. On the upper level are cells with high narrow windows where common criminals are confined together. The second level has smaller, personal cells without windows for highborn captives. Torches in the halls casting light through the bars. The third level cells, the "black cells", are smaller still, and have doors of wood so that no light enters them. These are reserved for the most vile and dangerous prisoners. The lowest level is used for torture. It is supposedly safer to go through the fourth level of the dungeons in darkness, because there are things one would not wish to see.
The Red Keep has a network of secret passages and tunnels. King Maegor had them built to ennable him to make a quick escape should his enemies ever trap him. The tunnels are supposedly full of traps. Some tunnels are of stone, while others are earth supported by timbers. Some of them are so small that a grown man must crawl through them. Some pass very close to other rooms in the Keep, allowing a hidden person to eavesdrop on conversations. One secret passage leads from the bedchamber of the Tower of the Hand to the outside. The bedchamber used by Varys contains a secret lever that causes a stone slab to float up and reveal a staircase. There is also a secret way to get out of the Red Keep onto the cliffs facing the sea. Narrow handholds, impossible to see from the ground, have been cut into the rock so one may climb down to a trail beside the Blackwater.