The Sinking Ring of Ku Pum

Ku Pum was a sorceror of the great estuary land of Wu Karu, and dwelt on the Isle of Trum Pku, which is the easternmost of the isles in the inlets of Wu Karu, into which the tide rushes each day, and rushes out. Trum Pku was a very empty island, for Ku Pum was known to truck with beings of the Outer World which are not advisable to take meat and drink in the company of. Ku Pum was a strange man, and while he lived he made many odd devices such as sorcerors make, and in his making, created quite a few devices of strange magic, tied to esoteric uses but very useful in their respective fields.
Such an item was the Sinking Ring of Ku Pum, which has been long in the keeping of Ba Bing, Ku Pum's only daughter, who dwells in the city of Po Karu, which is the chief city of Ku Waru.
Ba Bing relates this tale of the ring's making:
Ku Pum was in a mood of making, such as he often was in that time, and in this strange need, he sacraficed seven digging-birds and seven mud-fish, and seven stones of little value, burning them in a fire of sorcerous heat, which was quenched with ape's blood. The fumes from this fire where captured in glass pane, and this pane was shattered with a stone mallet, and the sound of this shattering summoned Stone Bell, a Spirit of caves and underground places.

Ku Pum said to Stone Bell: 'In my need, I require your aid. Is my sacrafice sufficient?'

Stone Bell said: 'Yes, though you are mortal. What need have you?'

Ku Pum said: 'It is my need that I have a shaft, to be sunk into the ground of my island, so that I might more easily make sacrafices to Spirits tied to the Earth, such as you.'

Stone Bell said: 'This is an easy thing.'

The Spirit reached into the stone of Ku Pum's tower and drew forth a ring of smooth, uncarved make.

Stone Bell said: 'This shall serve your need. Good day, mortal lord.'

Ku Pum said: 'A thousand thousand thanks; but that other makings were so easy.'

Magical Properties:

The Sinking Ring of Ku Pum is a small stone ring, smooth and grey, with no marks of any sort, save Ku Pum's mark, which he carved into it.

The Sinking Ring has a curious property- when placed on a surface, and give the command word ('pemu', Karu for 'go')the ring sinks down through the surface, digging out a smooth, tiny shaft, about large enough for an arrow to be dropped into, and continues to sink until it is recalled with the command word('dupu', the Karu word for 'come'), or until it no longer feels resistance(for instance, if it fell into a cavern while tunneling through the Earth). The Sinking Ring will tunnel through any surface, save for metal. If commanded, the Sinking Ring will tunnel through any non-metal thing, including flesh. However, the Sinking Ring will always float onto the top of water, and will never sink in liquid; this may make it useful if one is lost at sea.