From “Seven Swords” by Ed Greenwood (Dragon #74, June 1983), there is mention of a sword that floats in just about any liquid you place it into: Namara, aka “The Sword that Never Sleeps”. How to make this an encounter location?
1. Transfer the property of the sword to a body of water. Maybe the sword (and its bearer) drowned in a lake–or better, fell to her death in a deep pond.
2. The sword bearer was an adventurer. She possessed a magical ring that could push water away out to fifteen feet, and create a pocket of everlasting air in its place.
3. Her companions drowned along with her after she went over the muddy edge of a deep shaft at one end of the pond, taking her sword and the adventurer’s means of breathing underwater with her.
4. Absent any water to slow her fall, down she went to a bone-shattering landing at the bottom. She managed a painful crawl partly into one of the six or so tunnels that led away from what was once a landing from which dark elves levitated upwards to the surface world, before she succumbed to her injuries.
5. So the adventurers found the ruin they were looking for–it just killed them quickly, all thanks to a little bad luck. The body of the sword bearer is still encased in a bubble of air, and has rotted oddly in the wet muck where she died.
6. Forty years or so later, the Spellplague struck. In the case of the sword bearer, the magic of her sword was swept away in the magical chaos, and dispersed into the natural rock shaft that had served well as a tomb for bold adventurers.
7. One of her fellow adventurers wore magical chain armor that was stripped of all its enchantments by the Spellplague, save for its ability to not rust, and in time what was left of his soggy corpse floated the 20 or so feet to the surface from where it lay.
8. Some years later his body was discovered and the armor looted. Word of the find slowly spread through the woods where the pond was located (let’s say the King’s Forest, in Cormyr, several miles west of Dhedluk).
9. Today the pond remains a curiosity. Experienced foresters hire out to lead adventurers and anyone with time on their hands and a desire to explore the safer parts of the King’s Forest to the pond.
10. Visitors find that the rumors are true: The murky pond water will not admit anything made of iron or iron alloy below its surface without some effort made to push such objects under water, and when those objects are released they float straight up to the surface. A warrior in full plate can lay on the water and sink only an inch or so in, as this is the equivalent of wearing a body-suit made out of life jackets.
11. Water removed from the pond does not retain the quality of keeping iron objects afloat.
12. Efforts to dredge the pond with stone implements tied to ropes turned up bone and decayed clothing and items from two other corpses (other comrades of the sword bearer), and led to the discovery that one end of the pond is quite deep–longer than the 50′ of rope used to dredge. This much is common knowledge to those who’ve visited the pond or talked to others about it.