Mu, or Lemuria, refers to a continent which is hypothesised to have once existed in the Pacific Ocean. It is said to have been the origin of the civilisations of ancient India and Tibet, and of the Incas and Mayans, all of whom are said to have been colonies of Mu (indirectly in the case of Tibet, which is said to have been settled via India).
The moai, the carved stone heads of Easter Island, are said to be relics of this culture, just as the Pacific islands are the remains of the continent. Mu is said to have been destroyed by volcanic eruption and earthquake, followed by flooding. Rather implausibly, Mu is said to have been "completely obliterated in almost a single night." Some have suggested that Mu was more advanced than the modern world, and that the destruction was the result of some weapon or technological disaster, such as a nuclear war.
I would suggest that a more realistic theory is that Mu lay in the same land as Teleleli. Perhaps the city itself lay within the boundaries of Mu, perhaps not. It seems likely that Mu itself was not destroyed, but merely the 'bridge' between it and our world. Given my speculations about the link between Teleleli and the Biblical land of Sheba, it may be that this loss occured in pre-Biblical times, and the legend of the expulsion from the Garden of Eden arises from the experience of a distant colony suddenly finding itself cut off from home, trapped in a dismal frontier. Similarly, we might find it profitable to study the ancient Egyptian concept of the afterlife as a distant land, and the ancient Indian Uttarakuru, a fabled continent which is sometimes described as existing in our world, and sometimes in another.