Beowulf was written down by Christians. It does not mention any god other than the Christian one, although it refers to fruitless offerings to other gods, see lines 170-188. Presumably to the mind of the person who wrote down the poem (in all probability a monk), the Danes would not have been afflicted by Grendel if they had been Christians.
The castle in Macbeth is called Dunsinane Castle. It is the final stronghold of Macbeth where he makes his last stand against the forces of Malcolm and Macduff.
Duncan's decision to name his son, Malcolm, as his heir instead of Macbeth, and his decision to stay at Macbeth's castle without informing him both upset Macbeth.
The forest outside Macbeth's castle is called Birnam Wood.
The soldiers are on night watch at the castle in the opening of the play "Macbeth." They are accompanied by Banquo and Macbeth.
If by "the Macbeth book" you mean Shakespeare's play, Macbeth stays at various castles. The castle where he murders Duncan is at Inverness (It's on Loch Ness in the northeastern part of the country) The castle where he is attacked by the English army supported by the Scottish exiles is at Dunsinane Hill, about halfway between Perth and Dundee and straight north of Edinburgh on the east coast of Scotland
Macbeth kills Duncan in his own castle at night time.
There are a number of castles in the play: Forres, Inverness, Fife and Dunsinane. Inverness is actually Macbeth's castle.
Macbeth's castle
In Act 1 they are living in Inverness, possibly in a castle or possibly in a large house. By Act 5 they are living at Dunsinane, which is a castle.
Macbeth's coronation
Glamis Castle.
MacDuff and Lennox knocked at the main entrance of Macbeth's castle to gain entry.
Macbeth brings back King Duncan's bloody daggers to the castle after he murders him.