Dream of a stranger, a key, and a train

"I dreamed about a man I didn't recognize, although in the dream I felt like I knew him. We were sitting in a small cafe, but I can't remember how I got there. He was talking to me about something important. I could see his face clearly, but the words kept getting mixed up. At one point he gave me a key and told me I needed to keep it safe. I asked him what it was for, but he just smiled. Then suddenly we were walking through a house that felt familiar. He was ahead of me, opening doors one after another. I kept thinking I had been in that house before. Then I looked away for a second and he was gone. The key was still in my hand. I walked outside and somehow ended up at a train station. I remember feeling like I needed to find him before the train arrived, even though I had no idea where he had gone. I woke up still thinking about the key."