This guide is suitable for current RuneScape and Old School.
Talk to King Arthur, who can be found in Camelot castle.
Ask him if he has any quests, and he will tell you of one that is very dangerous. He asks for you to search for the Holy Grail, and will advise you to speak to Merlin for further direction.
Finding out about the Grail
Merlin is found on the first floor on the castle, next to the library. He will tell you that the Grail is most likely to be found somewhere holy, and there is a island that may be of importance however he has forgotten the name of it. He will also suggest speaking to Sir Galahad, who lives west of McGrubor's Wood.
Head to Entrana, which can be reached by taking a boat from Port Sarim. Enter the church and speak to High Priest regarding your quest; and he will inform you that the Grail has once passed through the land, but he no longer knows the location nor cares. However, a Crone will interrupt the conversation telling you of information that will aid you in your quest. During the conversation with her, be sure to ask all the questions presented.
After learning of this information, head to Sir Galahad, who lives west of McGrubor's Wood. After some conversation he will give you a holy table napkin, and a cup of tea.
With the napkin in your inventory, head to Draynor Village mansion and climb to the top floor where you will find two magic whistles on the table. Pick them both up, as the second whistle will be needed later on in the quest.
Note: Level 120 fight ahead; be prepared with food and armour.
Make your way to Brimhaven, and head to the area with the gold rocks shaped like a horseshoe. There should be four poles nearby, stand under them and blow the magic whistle.
Black Knight Titan
You will notice a bridge guarded by an level 120 Black Knight Titan. You will now have to defeat him to cross the bridge. You may attack him with whatever weapon, however you must make the finishing blow with Excalibur.
After the battle, cross the bridge and follow the river to come across a Fisherman. Talk to him and ask how to gain entry to the castle, and he will tell you that you will need to ring a bell.
Head up to the castle and pick up the grail bell, and ring it. You will magically be whisked inside. Climb up the staircase and talk to the Fisher King. Tell him you are searching for the Holy Grail, and he will tell you that it is inside the castle, however it cannot be taken. Ask him why he doesn't look so good, and he will tell you that he is dying and will ask you to locate his son, Percival.
Blow the whistle, and then return to Camelot and talk to King Arthur. He will tell you that Percival is a knight of the round table, and that he is on a quest to recover the Golden Boots of Arkaneeses, and has not yet returned. King Arthur will then give you a magic feather, and will explain that by blowing on it, it will lead the way.
Blowing on the feather will lead to Goblin Village, which is north of Falador. Search a nearby hut to find sacks with an option to 'prod.' Open the sack to free Percival, who will explain that he fell into a Goblin trap and was forced to act as their slave, before they put him in to a sack and forgot about him. Tell him that his father wishes to speak to him, and you will give him the second magic whistle.
Return to the Fisher Kings' Realm by heading to Brimhaven and blowing the whistle under the four wooden statues. Enter the castle and talk to King Percival who will tell you that the land magically restored itself when he accepted the crown.
Climb downstairs, and go up the eastern staircase to the third floor, where you will see the Holy Grail. Take it, and return to King Arthur to complete your search for the Holy Grail.
Congratulations! Quest Complete!
Guide Made by: DaDa
Corrections submitted by: Doctor Shemp, DaDa, Ashwin, Dx1438, Power of Five, Amor