Most travelers to Spain's La Rioja wine country focus on its gleaming wineries, made ultramodern by today's star architects: Frank Gehry's pink-and-gold-titanium Marqués de Riscal; Santiago Calatrava's wavy-roofed, sculptural Bodega Ysios; Zaha Hadid's flask-shaped wine-tasting pavilion at López de Heredia. But almost nobody visiting La Rioja goes backward in time, into the dank underground caves of Marqués de Legarda, a winery hewn by the Royal House of Navarre in the twelfth century. Nor do they have the chance to sample its vintages, which are served only in Madrid's finest restaurants and occasionally at Royal Palace events, or the opportunity to visit the winery's adjoining palace, originally a castle built by the Knights Templar and now a 33-room heirloom of the Royal House of Navarre. Here, among priceless relics dating from the twelfth through the nineteenth centuries, is a museum's worth of unique objets, each with its own colorful history: portraits of generations of illustrious Navarre ancestors; collections of ancient books (including early editions of Don Quixote); the office, desk, papers, and coin collection of D. Martín Fernández de Navarrete (1765–1844), war minister to King Fernando VII; the bedroom of a seventeenth-century bishop who was confessor of the queen of Spain; Belgian tapestries; Murano chandeliers; hand-carved ivory bargueños (cabinets) hiding secret drawers; and trompe l'oeil "wallpaper"—actually painted by hand—concealing secret doors.

This "museum," however, is not listed in any guidebook. Nor do museum rules apply: Not only was I allowed to touch and photograph all its treasures, but I actually dined in one of its rooms—with Martín Fernández de Navarrete (or Martín Legarda, as he is known), the 45-year-old first-born son and heir to the Marqués de Legarda, and a descendant of the legendary chevalier El Cid. I sat at his medieval-scale dining table, his family's ornate antique linens and silver at my fingertips, eating his (well, his housekeeper's) traditional home cooking. Each course was paired with a classic Rioja made by Legarda himself in his adjacent winery—which is also not in the guidebooks. Like the palace, the winery is closed to the public.

So how did I get in there? It has nothing to do with my position as an editor at Condé Nast Traveler. Anyone visiting Rioja can follow in my footsteps—as long as you know the right person to call, show sufficient intellectual curiosity and appreciation, and can afford the price tag. I had heard about the experience through Spain specialist Virginia Irurita, of the Madrid-based travel agency Made for Spain (she's on my annual list of the world's best travel specialists). Irurita, who can open doors in Spain that others cannot, has known Legarda since they were both seven years old. Today, when her clients are headed to La Rioja and are eager to see a part of the region's history that is not on the tourist trail, she sends them to her friend's country estate.