The Fog
The continent of Lorica is surrounded by a perpetual, dense fog. For reasons unknown, it always takes exactly 20 days to sail through the Fog, even though it doesn't appear to maintain a constant size. At times the Fog is as far as a 5-day voyage from shore; at others, it creeps to within 2 days.
Although no two voyages through the Fog are alike, a few common threads have emerged from the reports of sailors and settlers:
Ships move through the Fog at a constant pace, but there is usually no wind.
A diffuse light illuminates the Fog during the day and wanes to a dim glow during the night, but the sun, moon, and stars are never visible.
Navigating the Fog requires supernatural guidance.
The Fog tends to induce disturbing hallucinations.
Strange creatures and phenomena have been known to appear in the Fog.
Several ships have been lost in the Fog.