As the attacker would have got much closer to the castle he would have seen the ditch and curtain wall. The ditch was a good form of defence because it was hard to get out of once you were in it especially if u were carrying lots of armour. If it was raining it would have made the ditch all muddy and slippery, making it almost impossible to get out of. The curtain wall was a high wall surround the castle and the ground that it was in. this was a good defensive feature because it was hard to get in to the castles grounds through it as it was so high.
If the inner wall was pulled down then the attackers would have had to tackle the doors and windows. As these were the only ways into the castle they were heavily guarded. The door was on the first floor of the castle. To get up to it you had to climb up some steps. These had a sharp turn in them near the top of the steps so if you wanted to use a battering ram to knock the door down it would have been very difficult. Before the door there was a gap which was usually crossed when the drawbridge was down. But when being attacked the drawbridge was closed. If some how the attackers got the drawbridge down there was a portcullis that they had to get through. If they did then they entered the fore building. This room was very small and had a sharp bend in. Again this meant it was hard to get a battering ram in. to get out of the fore building and into the castle you had to go through yet another portcullis and a thick wooden door. The windows in the castle were very effective too. At the bottom of the castle the windows were very thin. Thick enough to shoot an arrow out of, but thin enough to stop someone crawling in through one. The castles windows got wider the higher you got up the castle.
Once that the attacker got into the main keep through the fore building they only reached the offices and storage space. The attackers still needed to go up the stairs to the first floor to get to the main hall and the main living area. The stairs were designed well so that the attackers could only fight with their left hand when going up then. They also had the disadvantage because its harder to fight up than down. The stairs were also quite steep and they were spiral stairs. This made it very difficult to fight people when going up the stairs.
Meanwhile outside the castle other attackers would be trying to get into the castle through the roof using scalene ladders and siege towers. These were no good because of the walls and batter. The ditch also prevented the attackers from using the siege towers. This also made it easier to for the defenders to attack the attackers by throwing hot oil down on them and using the battlements to their advantage, firing arrows out of them.
Although the castle had many strong defensive points it also had its weak points. For example, at times of siege they had a constant water supply but when their stores of food ran out they would have had to surrender the castle to the attackers. As the castle was also a square keep castle attackers could easily undermine the square towers. Then the attackers would have to surrender.
Over the entire castle was a good defensive structure but it had one very big weak point. And that was if the castle was put under siege then the defenders would lose the battle after time.