The Pool of Prophecy

In a hollow between the gnarled roots of three trees lies a small pool reflecting what dim light filters through the trees’ thick leaves. A trickle from the limestone hills above falls into the pool in a steady cadence, and a similar rivulet runs down toward the river.

The Pool of Prophecy is a location in the wilderness that can be inserted into any game with ease. (I concocted it last week for my weekly game.) My description above assumes several optional details (limestone hills above, a nearby river) which can be tweaked or removed as required.

The Pool shows the first sapient individual to gaze into it strange things.

An example:

A ripple runs across the pool’s surface, though the breezes through the forest branches seem to still. The reflection is not what you expect.

A great tree, knotted and ridged trunk dwarfing those around it, reaches its millions of slender leaves toward the new moon. Suddenly, a blinding un-light of the deepest black smothers the air, and the mighty giant’s leaves fall as ash to the dying earth.

A ripple runs across the pool’s surface. The reflection is new.

A bent figure, clad in hides and crude cloths, steps from the brush into a shaft of pale moonlight. It begins a slow tattoo on an oval drum of stretched hide, which builds menacingly into chilling polyrhythms. The edges of the vision begin to dim even as the figure drops the drum, stretches, contorts, and stands on all fours. It has antlers.

A ripple runs across the pool’s surface. The reflection is new.

At a lake’s bottom, clear but dark, lies a skull. Beside it, half buried in the muck, is a crown of twisted, pointed iron. A dim shadow is seen on the benthos - a figure swimming. Growing larger.

A ripple runs across the pool’s surface. It reflects only quivering leaves and dim stars. 

The repetitions and kennings set a dim and surreal mood, but what potentially has the most impact is the last line. Yes, when the vision(s) are complete, it is always nighttime, and the stars are always visible. Any outside observers besides the party notice no difference in the passage of time, and the party experiences none of the effects of several hours of passed time (hunger, sleepiness, etc.) - they just look up and notice that it was night, though it may have been day when they peered into the Pool. 

The Pool will not function until the sun has risen once more.

Place the Pool in a remote location, one the players will not be able to return to often.

The Pool cannot be affected by touch or artifice: cups and bowls pass through it and emerge dry as if the pool weren't there, and it flows around or pours through dams or other placed obstacles. A player character who attempts to touch or drink from it experiences a faint sensation of cold-warmth, but that is all.

Use the Pool to plant the seeds of plot hooks and important lore in the minds of players. It is best if the visions are unclear at first - but when the players discover what they refer to, the "aha!" moment should be worth any effort. I used three visions since I had several points I needed to prepare the players to discover, but one vision is fine. (My visions also proceed in order of past, present, and future, which is cool but not strictly necessary by any means.)