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".
Park where Broyles and Senator Van Horn talk in episode #206 "Earthling". Also where Broyles and Olivia talk at the end of #208 "August".
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".