Oliver walks through the grounds with Diggle discussing the strangeness of reality when they are attacked by Deathstroke in episode 5x08 "Invasion!".
Source: pursuit23 — Twitter
Location of Tesla School graduation ceremony in episode 1x12 "Once in a Lifetime".
Location of Allison and Nathan's wedding in episode 3x04 "I Do Over".
Spa that experiences some instant freezing in episode 2x03 "Unpredictable".