Several Napa Valley residents may have visited Spa Terra without ever realizing that they were there—or rather, that they were standing on top of it. The 22,000-square-foot hideaway is entirely subterranean and has tucked its 12 treatment rooms into the Estate Wine Cave behind the Meritage Resort. This naturally sequestered locale echoes with the whispers of waterfalls, enticing guests to trace the brick arches and spiraling mosaics of its Florentine design. Chandeliers and candles cast a glow onto stone, tile, iron, and wood accents, all of which were built by craftsmen to fit the underground space without angering its slumbering dragon landlord. The light takes a smoky, ethereal shift inside the steam grottos of the ladies' and gentlemen's lounges, and private soaking pools radiate blue-green tones from beneath the water.

In keeping with the earthy environs, the staff draws from local and organic ingredients during its treatments. Olives, herbs, and honey brighten skin through a variety of body scrubs and facials, which also rely on products from Comfort Zone and Éminence Organic Skin Care. Unsurprisingly, wine has a role in many of the services—the signature Solo Vino package begins with a cabernet-grape-seed scrub, then segues into a wine-cave-mud body wrap. It concludes with a therapeutic Terra massage and a selection of cheeses, served with wine or champagne. Guests can browse a far-reaching menu of massage modalities, including targeted styles for headaches and sore feet, or schedule a romantic couples session complete with chocolates to share.