Roadside Picnic is a 1972 soviet novel by the Strugatsky brothers. I'm not going to explain the whole plot, so check out the Wikipedia page.
The book is damn good. Not much else to say there.
What I enjoy most is the content inspired by it.
The 1979 film Stalker by Tarkovsky is fantastic. It's a beautiful movie, and while it's different from the source material, it is amazing on its own.
The S.T.A.L.K.E.R. series of games is a personal favorite of mine. Nails the feeling of melancholic isolation that the film and book does.
Otherside Picnic is a novel/manga/anime inspired by Roadside Picnic. It's also gay, which is cool I guess.
That's all. I like Roadside Picnic and the inspired media.