My friend and I agree that this was the standout highlight of our week in Berlin, and a real hidden gem. For €10 apiece with student discount, we were treated to a two-hour-long tour of Berlin's underground past. Our enthusiastic, gregarious guide, Laura, informed us about the history of escape and espionage surrounding defectors from East Berlin to West, as we worked our way through the labyrinthine corridors of an abandoned metro station and a hollowed-out brewery. These settings really added to the experience, and it felt as much an adventure as a tour. We learned of double agents, superhuman efforts to overcome hardship and the power of romance. To summarise, this is a fantastic hidden gem that will enchant any history enthusiast!