Following the infiltration of the Trust by the Goa'uld and the defeat of the System Lords, Ba'al settled on Earth and began rebuilding his power base by taking control of corporate and financial institutions such as Farrow-Marshall and Hammel Technologies. He was also behind the building of the Halcyon Tower, a skyscraper in downtown Seattle that was less than a month old. As a precaution, he had seen to it that the entire superstructure of the building was laced with naquadah, making it, in effect, an enormous bomb.
Ba'al was being hunted by the SGC and NID as well as Jaffa who served Gerak. After Ba'al had escaped a raid on Farrow-Marshall headquarters, he used his connections as head of the Trust to learn that another attack was being planned against his compound, and he announced that unless the intended strike was called off, a bomb in the Halcyon Tower would be detonated at 1:30pm local time, which allowed a window of only 45 minutes.
Despite the threat, both the NID and the Jaffa launched independent attacks on Ba'al's facility as the SGC attempted to evacuate the Tower and locate the detonator in time to disable the bomb. Readings indicated that naquadah was present everywhere, however, and once it was determined that the entire building was the bomb, there was not enough time to find the detonator or evacuate the area. Instead, Prometheus used the Asgard transport beam to beam the entire building into space where it exploded harmlessly above Earth's orbit.
The disappearance of the Halcyon Tower left many questions afterwards. Julia Donovan of "Inside Access" was among the members of the media broadcasting from the building site. Because the building had been evacuated, there were no eyewitnesses, and the official cover story attributed the building's disappearance to a gas line explosion, although the pile of rubble that remained was not enough to account for an entire building. Conspiracy theories abound.
Episode Reference: Ex Deus Machina