Duncan goes to Macbeth's castle in Act 1, Scene 6.
Ducan is highly impressed by Macbeth's act of honour, loyalty and courage, as shown during the battle introduced to the readers in the introductory scene. Duncan falls in Macbeth's favour, when the wounded captain/officer informs him about the courage showed by him, when Duncan's army faces a dbouble attack by the Norweign lord. Duncan is now completely convinced about Macbeth's love and loyalty towards him and can not stop praising him. thus, in order to congratulate Macbeth, Duncan approaches Macbeth's castle along with his noblemen. Duncan bears a gift for Lady Macbeth. In the Elizabethan era, when a king would come down to a nobleman's castle, it would a news of great honour, a sort of blessing for the nobleman. This was because in those days a king was considered to be the representative of God on earth.
(BASIC POINTS REQUIRED TO BE EXPLAINED FOR A 20 MARK ANSWER= SECTION B. ISC)