"Roadside Picnic" is a science fiction novel written by Arkady and Boris Strugatsky in 1971. The novel was first translated to English in 1977 by Antonina W. Bouis. By 1998, 38 editions of the novel had been published in 20 countries. I have read it countless times. Here's a PDF, in case you've never had the pleasure:
http://soviethistory.msu.edu/wp-content/uploads/2015/10/picn...