Ultima IV: Quest of the Avatar/The Strongholds of the Principles

Open quests
Romasco of Skara Brae started a thread about the Great Stygian Abyss. He sent the companions to Zair the Wise in Paws who, in turn, directed them to his brother Zair in "a village beyond Lock Lake".

Jingles of Paws spoke about the "Gate Travel" spell and directed the Companions to his master Mentorian in "a village beyond Lock Lake".

Zorin of Castle Britannia told the Companions to visit the three castles and speak to all named Antos. Then, if you go to the nearby Castle of Love (Empath Abbey), the people there direct you to "the village beyond Lock Lake", too.

Two more characters in Castle Britannia, Joshua and Juliet, spoke about an Axiom riddle. More on this can be learned... in that same village of Cove, of course!

In the NES port, the mage in castle Britannia (Zorin) is the only character who was kept the same. A ranger in Castle Britannia (Zair from Paws) just hints at the village of Cove, but the "Word of Power" was omitted from this port. The "Axiom Riddle" was omitted, too, therefore the two corresponding characters in the castle (Joshua and Juliet) speak about other subjects. A man in Paws (Jingles) teaches a new spell, but Mentallion (Mentorian) anyway waits for you in Cove.

The whirlpool
Well then, how can we cross Lock Lake?

In the NES port only, two inhabitants of Buccaneer's Den reveal the secret to reach Cove: the barkeeper (The Captain) and a pirate in the pub (J. J. Scirlock). Leave a 100 GP tip at the pub, and learn about the link between the whirlpool and Lock Lake.

The whirlpool moves randomly around the seas, but because of this randomness it generally remains in the same area. Apparently, it can be often found in the sea between Jhelom and the Shrine of Honor (e.g. Amiga and Master System ports), but it can also get past Cape of Heroes, south of Trinsic. In the NES port, it is more frequent to find the whirlpool north of Buccaneer's Den, south of Lock Lake river mouth.

The magical ship wheel
This item is not included in the NES version, because the ship in that port has no HP (Hit Points or Hull Points).