In sci-fi book "Monday begins on Saturday" by Arkady and Boris Strugatsky there was cool, but rather unrealistic theory, according to which Tunguska event was a

In sci-fi book "Monday begins on Saturday" by Arkady and Boris Strugatsky there was cool, but rather unrealistic theory, according to which Tunguska event was a landing of an alien spaceship, which had reverse time arrow. They landed and then have gone to our past, finding themselves in the untouched ancient taiga, and leaving no traces in our future.