The Omega Stone is a PC puzzle adventure game developed by Omni Creative. It was the sequel to the game Riddle of the Sphinx and was released by DreamCatcher Interactive on March 19, 2003. In The Omega Stone, players embark on an adventure to solve an ancient mystery, visiting locations such as the Great Sphinx of Giza, Stonehenge, Easter Island and even the ruins of Atlantis in the process. You travel to these sites with the use of passes where you investigate the area for clues on the location of 5 "Omega Discs". The locations of these, in addition to those already mentioned, include beneath the Bermuda Triangle (although where is unknown), inside the manor of an English Lord, inside the pyramid of Chichen Itza and a within a Druidic Compound.
Source: Wikipedia, "The Omega Stone", available under the CC-BY-SA License.