Is there any book you can read over and over again without ever getting sick of it? Do you discover something new every time you read it?
Several. Lord Valentine's Castle by Robert Silverberg is one. Lord of the Rings is another. Pride and Prejudice, A Fire Upon the Deep/A Deepness in the Sky, and Brian Daley's Floyt/Fitzhugh "Third Breath of Man" series (Requiem for a Ruler of Worlds, Jinx on a Terran Inheritance, and Fall of the White Ship Avatar). Probably a dozen more, actually.