I love these kinds of books. A few suggestions:
- Randezvouz With Rama by Arthur C. Clarke
- Roadside Picnic by Arkady and Boris Strugatsky
- Solaris by Stanisław Lem
- House of Leaves by Mark Z. Danielewski (not sure about this one, haven't read it yet.)
- Ringworld by Larry Niven
Hope you find something that fits your tastes and looking forward to other suggestions.