Source: Julie Holden — Twitter
Hook and Cora arrive in town in their invisible ship in episode 2x10 “The Cricket Game”.
Jonas finds some mysterious tire tracks outside the abandoned building and SG-1 investigates to find a spaceship under construction in episode 6x05 “Nightwalkers”.
Source: Stargate SG-1 Locations
Thawne, Darhk, and Merlyn arrange a meeting with Al Capone to propose and alliance in episode 2x08 “The Chicago Way”.