Drink from the Horn of Balmythria

The Horn of Balmythria is an actual dragon horn that a famed silver dragon lost in battle against the Gygans. It was recovered by the priests of Mytros and consecrated by The Five. It reputedly has many magical powers including the ability to grant visions to those who drink from it. The horn was stowed in a reliquary in The City of Estoria .
The Heroes of Prophecy tracked the horn to The Mossy Temple after it had been stolen. It lay deep within the underground temple, laying atop a feasting table, guarded by a truly grotesque boar-satyr monstrosity. The battle was hard fought, but the Chosen came out victorious, claiming the Horn for themselves.
Once outside the tomb and rested, the party took turns drinking from the Horn, and subsequently all passed out, sharing a vision of the high seas:

You are standing on the deck of a beautiful galley.

A bright cerulean sea stretches out before you. You
look down at a strange bronze device in your hands.
It seems to reflect the constellations of the night sky,
even though the sun shines brightly overhead.
The oarsmen pull the ship through the water faster
than you thought possible. You look down at the men
on the benches. They meet your gaze with dead eyes
and skeletal faces—dozens of leering corpses.
You are startled awake.