One of the questions on thought experiments that has been debated in the literature is whether they can be said to deliver any new knowledge, and, if so, how they do that. In the words of Thomas Kuhn: “If we have to do with at real thought experiment, the empirical data upon which it rests must have been both well-known and generally accepted before the experiment was even conceived. How, then, relying exclusively upon familiar data, can a thought experiment lead to new knowledge or to new understanding of nature?” In this talk I will present some, in my opinion, impressive thought experiments in Physics. In light of these, I will then touch upon the issues mentioned above. I also look forward to a lively discussion with the audience!