Go to 'Merlin's Laboratory' in Camelot Castle, ASK MERLIN EXCALIBUR.
Now go to 'Dynas Emrys' near Snowdonia and ASK MERLIN EXCALIBUR
Now go to 'The Lone Fortress of Tintagel' (near Morgana), then DOWN, ASK MERLIN EXCALIBUR
Now go to 'The Sword in the Stone' (near Folkington), ASK MERLIN EXCALIBUR
Finally go to 'A Rock Promontory over Llyn Ogwen' (SWNNE from Owain), ASK MERLIN EXCALIBUR
Completion of this quest also gives you the following 3 stat quests and the whois for each in place of the Greece Stat quests:
+3 Strength
+3 Constitution
+3 Dexterity
Note: This is also how you activate the stonehenge era transitions. Once completed you can walk north from Stonehenge to get to 'The Dusty Crossroads' in Tara, south to get to the 'Docks of Casablanca' or east to go to 'The Monkey Inn' in China.