Leave Moorgate to the north, and go up the causeway until you find the Glowing Shrine. You might find it in your best interest to have high swimming, or to fly or walk on water.
On the West Causeway
A small lighthouse lies off the coast to the west of you. The road provides you no way of getting to the small building. Perhaps there is another trail you can locate. Obvious Exits: North South West Glowing Shrine is offering a quest (use SHOW QUESTS)
Go west, then use the command SWIM. Then go north west and you are at the base of the Lighthouse. You can lure here, without a need to enter the Lighthouse itself.
The Sea Wyvern
The Sea Wyvern is below the Lighthouse, in order to fight it you will need to be able to breathe water, and to defeat the Water Dragons which accompany it you will need to be able to fly. You can get an adventure token drop here.