"Seest thou not How thy Lord dealt With the 'Ad (people) -- Of the (city of) Iram, With lofty pillars, The like of which were not produced in (all) the land?" (The Noble Quran) 89:6-8
Ubar is believed to have been built by King Shaddad Bin Ad. The Ad were believed to be a tall race, and the city is believed to be founded around 1000 B.C. The city is believed to have sunk down into the sands of present-day Oman as a punishment by Allah around 300 A.D. because of its inhabitants' sins.
The search have been going on for 10 years now and evidence is slowly building up on this fable.
People like to call it the Atlantis of Arabia, difference is that Atlantis sank under the sea and Ubar sank under the sand.
Nasa Observatorium: http://observe.ivv.nasa.gov/nasa/exhibits/ubar/ubar_0.html