Hook and Cora arrive in town in their invisible ship in episode 2x10 "The Cricket Game". From episode 2x11 "The Outsider". From episode 2x13 "Tiny".
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".
Source: Julie Holden — Twitter