In an alternate future, Earth was a member of the Aschen Confederation, the SGC was a tourist attraction, and the stargate was housed at the J.R. Reed Space Terminal in Washington, DC where it was open to the public and used routinely for space travel. The last heavily defended place on the planet, it was protected by automated defenses and laser beams. SG-1 died breaching the defenses in order to send a note back in time through the stargate that would change their history and prevent the extinction of the human race by the Aschen.
Location: Plaza of Nations
Cross Reference: Aschen, Time Travel 2010
Episode Reference: 2010