Computer Science (CS) Unplugged activities are designed to engage students with CS concepts. It is an active learning approach combining physical interaction with visual representation. This research article investigates the impact of CS Unplugged on students' understanding of the bubble sort algorithm. Algorithm visualization, traditionally employed for active knowledge construction, serves as the foundation for this approach. The research was conducted as a quasi-experiment in middle and high schools in Split, Croatia, among 204 students. We divided the participants into two groups: experimental (CS Unplugged) and control (traditional teaching). The study included pre-test, mid-test, and post-test assessments. While CS Unplugged did not significantly affect students' understanding of bubble sort, it positively influenced long-term retention of the algorithm. These results highlight the potential of CS Unplugged activities as an effective teaching approach for CS concepts, specifically in promoting long-term retention of the bubble sort algorithm. The study also revealed misconceptions that included restarting comparisons after each swap, assuming the largest element reaches the end after one swap, and repeatedly swapping the largest element with its neighbor. Addressing these misconceptions through active learning activities like CS Unplugged can contribute to deeper understanding beyond memorization.