We had made arrangements with the host to check-in around 2 A.M. Host said that would not be a problem and that he would leave the key at the kitchen window where we could retrieve it by opening the kitchen window from outside. When we arrived at the house, our taxi driver stayed with us to make sure we got in and we are SO thankful that he did. We had no phone service, having just come to London. Thankfully, we were able to use the house wifi to contact airbnb, after all attempts failed to: open any of the windows, open the door, wake anyone in the house by knocking/banging on the door, and calling the host numerous times using our driver's phone. We contacted airbnb and they were not able to get in touch with the host either, so they recommended we find a hotel. Our 1s Airport Taxi driver who spent significant amount of extra time with us took us to a nearby hotel and would not take a penny. At the end, we were safe. The host said the key had been where he said it was all along. I am not sure what difference that would make if the windows would not open. He did say he was sorry the next day.