There were never two castles alike but they all had the basic idea and parts to them. The outer parts usually included the:
Outer curtain: the wall around the castle.
Drum tower: a round tower built into the exterior of the outer curtain wall.

The Moat: The moat was a deep ditch which might have been filled with water.
Outer Gate: This was where the drawbridge crossing the moat was.
Inner Curtain: This was the wall which you would face if you got through the outer gate, it was thicker and stronger than the outer curtain.
The Tower: This was where the most deadly weapons were. They ranged from archers to throwing stones.

Inner Gate: This was heavily defended and it had thick walls like the inner curtain.
Inner Ward: The inner ward was a large courtyard in the centre of the castle. This bit of the castle was defended by the keep which was a large castle like tower.

The keep: The keep was the safest part of the castle. If this was successfully breached then the castle was definitely lost.

Inner Bailey: The inner bailey was one of the strongest parts of the castle with thick and high walls.
The Dungeons
The dungeons original use was the keep which was the main tower of the castle and also the final defence point for the garrison to hide in when the outer walls were breached. It was the strongest or the only tower in the castle and in the lower part there were no windows so that made the walls stronger at the top. Even if this part of the castle was not comfortable it was safe but it was mainly used to keep the prisoners in. Although many dungeons now are just a plain room with a heavy door with the only entrance being a hatch door or trapdoor, the use of torture and being trapped underground has made dungeons a powerful metaphor.

The Latrines
Formally known as the garderobe in medieval times as the toilets were just rooms but they were positioned as far away as possible from the chambers and even had double doors just to reduce the smell for everyone. Unlike other rooms in the castle the windows had no glass, this was to reduce the bad odours as well. In the day time the windows would let light in and at night torches were set up so in the winter the garderobe would be freezing. The garderobe had wooden blocks with holes in, there were sometimes 4-6 of these in one garderobe. Under these blocks were chutes probably leading into the moat. As attackers may have used this way, there were iron grills fitted. Some of the larger castles had towers called latrine towers.
The Great Hall
The great hall was intended to be the main meeting place or dining area and was used by everyone in the castle. It was a large one room structure with a loft ceiling and would have been located in the inner ward. All the life in the castle would revolve around the great hall as all of the meals were served here. Pages and servants would also wait on the tables. As the place was so important, the servants made sure that it was clean and lighting was perfect. Entertainment was important in medieval times and many different acts would entertain all the guests. The person managing this would be the steward.
The decoration in the great hall was within the wealth of the owner of the castle. First the walls would be whitewashed, then the tapestries and coat of arms of the owners would go onto the walls. On the wall which had many colours, including gold paint which was at the time luxurious and so was used a lot.