Neutron Star
Hugo winner for the title story and the model hard-SF collection: the puzzle-story template (universe as antagonist, physics as plot) that defined the subgenre for a generation.
Series Guide
Known Space
by Larry Niven
Niven's engineered future history: Puppeteers, Kzinti, organ banks, Ringworld and a thousand years of humanity expanding into a universe full of other people's leftovers.
In the Guide
Ringworld
Hugo, Nebula and Locus winner; the genre's definitive megastructure, inspiring physics papers, the Halo franchise and fifty years of Big Dumb Object fiction.