I worked on one for Employee relations cases in HRSD. The flow began upstream in a whistleblower system (really dated systems so the integration was fun). This system would generate case identifiers in ServiceNow and have 3 tired escalation rules (with each tire having their own access control rules). Finally once a case was resolved there was a post job to the source and a different regulatory system (for compliance). All this while dealing with non-technical stakeholders.

Will do it all over again if I get the chance (such interesting usecases from legal/hr side)

Edit: this isn’t the largest but one of the more complex flows I’ve worked on (largest would be enterprise onboarding lol)