Blood and Wine, the latest (and final) DLC pack for The Witcher 3, has an Easter egg that I am frankly shocked anyone found at all. The secret is remarkably well-hidden, and not accessible through normal means.
Video: Here, courtesy of developer CD Projekt Red, is a new trailer for The Witcher 3's upcoming Blood and Wine expansion. Really, all they had to do was say "look, more Witcher 3." But this is cool too.