Ivanhoe by Walter Scott. I read an Oxford UP reprint of the novel, with many editor's notes glossing Scott's debt to medieval, Renaissance, and Biblical texts. He was evidently fond of Shakespeare. (The most fascinating nugget, to me, was the simplest: the etymology of the English word "lord".) The pacing is uneven (with a lengthy setup) and the dialog often laborious (though many novelists fall into that trap), but neither flaw can condemn such a pleasant read. Various historical points of color are anachronistic or wholly fabricated (well pointed out by the notes in my copy), and the plot does not order or explain events precisely as they occurred. Since I never read fiction to learn history, no such objections bother me. Indeed, the degree to which any fiction (however putatively realistic) is speculative is troublingly underrepresented, and we are often too unwilling to admit authorial meddling into fiction worlds not overwhelmed by aliens, spaceships, and high-tech (or no-tech) wizardry. (Thomas Mallon, writing in The New Yorker, made a more substantive yet similar point in the conclusion to his review of Stephen King's alternative-history novel 11/22/63.)
Scott's Scottish novels are his most highly-esteemed. My second dose of his historical elixir will be The Heart of Midlothian.