Barry travels back in time to recruit Snart to help with his heist of A.R.G.U.S. in the present in episode 3x22 "Infantino Street".
Cisco shows up in the forest for his fateful showdown against Caitlin in episode 3x22 "Infantino Street". Killer Frost is about to kill Cisco when Savitar shows up and says he needs Cisco alive in episode 3x23 "Finish Line".
The team investigates the final location that Edwin Gauss's pocket universe opened and find a bunch of hippies living in the woods in episode 4x18 "Lose Yourself".
Clifford and Marlize have a picnic and Clifford expresses his distaste for technology in episode 4x20 "Therefore She Is". Barry continues his search as the clearing where Clifford had his picnic with Marlize but runs into Ralph instead in episode 4x23 "We Are the Flash".
In a flashback, Laurel gives the eulogy at Tommy's funeral and later Oliver gives the eulogy at Laurel's funeral and reveals her identity as the Black Canary in episode 4x19 "Canary Cry". Oliver stands over Laurel's grave with Felicity in episode 4x23 "Schism".
Source: YVRShoots — Twitter
Oliver finishes burying Taiana while the last of the prisoners are airlifted out by Amanda Waller and A.R.G.U.S in episode 4x23 "Schism".
The team gets surrounded by suspicious rebels while heading to their camp in episode 1x13 "Leviathan".
The rebels come upon the ruins of the other rebel camp in episode 1x13 "Leviathan".
Amaya, Nate, and Ray head out the the Cretaceous wilderness in search of the missing temporal delineator in episode 2x13 "Land of the Lost".
The Legends travel to P.T. Barnum's carnival to identify and fix the anachronism in episode 3x02 "Freakshow".
A strange hooded figure raises Kuasa from a pond in episode 3x02 "Freakshow".
The Legends visit the cemetery where the vampire was buried and find an empty grave in episode 3x05 "Return of the Mack".
Young Stein lands in the woods and finds himself being chased by a gang of Vikings in episode 3x09 "Beebo the God of War".
Jax drops Stein back off in 1992 and gives him a letter to open in the future in episode 3x09 "Beebo the God of War".
Ray and Zari discover a body missing a heart in the woods and later the whole team assembles with a shirtless Gary to lure and banish the unicorn in episode 4x01 "The Virgin Gary".
Sara, Ray, and Kendra are returning to the Waverider when it takes off and leaves them behind in episode 1x08 "Night of the Hawk". The three Legends that were left behind discuss what to do next in episode 1x09 "Left Behind".
Sara and Ava watch a terrible 90s horror film where two camp councilors are attacked beside a lake in episode 4x04 "Wet Hot American Bummer".
Constantine sets up a protective circle around the camp while Ray is teaching the campers how to track through the woods and later Ava & Sara go after the shtriga in episode 4x04 "Wet Hot American Bummer".
Charlie and Constantine return to Salem to save the boys from the fairy godmother in episode 4x08 "Legends of To-Meow-Meow".
Park where Broyles and Senator Van Horn talk in episode #206 "Earthling". Also where Broyles and Olivia talk at the end of #208 "August".
Mel accompanies Nico to Trip's grave and Nico tells her that she doesn't believe the narrative of him being a killer in episode 1x05 "Other Women".