Constancy, humidity, chill. Such ideal aging conditions are just some of the reasons that Napa and Sonoma counties boast the largest concentration of wine caves in the world. Many wineries now strive to encompass their entire operations under the stealth of the earth, letting the vines grow above them. But caves are also beautiful, mysterious, scented of angel's share and marvelous places to visit and throw parties. Here are some of the more secret subterranean spots in the North Bay.

Napa

Atlas Peak Not open to the public, Atlas Peak is in the Mt. Veeder AVA and is known for its Cabernet. 3700 Soda Canyon Road, Napa. 707.252.7971. www.atlaspeak.com.

Baldacci Family Vineyards Open to the public daily, from 10am to 4pm. 6236 Silverado Trail, Napa. 707.944.9261. www.baldaccivineyards.com.

Beringer Vineyards This historic winery offers some seven daily tours for nominal fees, most of which end gratefully with a glass and take a spin through the underground wine-aging tunnels. Open daily, 10am to 6pm (summer hours). 2000 Main St., Napa. 707.963.7115. www.beringer.com.

Brown Estate Vineyards Brown Estate Vineyards completed the construction of a 6,500-square foot subterranean wine cave in 2005. Visitors are currently limited to wine-club members by appointment only. 3233 Sage Canyon Road, Napa. 707.963.2435. www.brownestate.com.

Chateau Boswell Winery This small, boutique winery is open by appointment only, selling most its wine directly via post to club members. 3468 Silverado Trail, Napa. 707.963.5472. www.chateauboswell.com.

Clos Pegase Clos Pegase's 2,800 square foot "cave theater" plays frequent host to parties, dinners, live entertainment and more. Free guided tours of the grounds are offered twice daily at 11am and 2pm. 1060 Dunaweal Lane, Napa. 707.942.4981. www.clospegase.com.

Constant Boutique Specializing in the kind of Cabernet that makes the Wine Spectator drool. The owners' former private residence, a historically protected building, is available to let. One assumes that a $16,000 monthly rent would allow occasional access to the caves. 2121 Diamond Mountain Road, Napa. 707.942.0707.www.constantwine.com.

Cuvaison Estate Wines Producing some 65 percent of its product as Chardonnay, Cuvaison has a 22,000 square foot cave, the Carneros Dining Room, that is available for parties. 4550 Silverado Trail North, Napa. 707.942.6266. www.cuvaison.com.

Del Dotto Vineyards Proud to boast some of the first caves in the Napa Valley, Del Dotto's were hand-dug in 1885 and restored in 1997. Del Dotto currently hosts candle-lit tastings, replete with cheese and chocolate, Friday-Sunday. Opera resonates until 4pm; rock rules after 4pm. Sounds like fun! The full cave experience with barrel tasting is $40 per person and reservations are required. A new tasting room is planned for St. Helena, currently held up by CalTrans work. 1055 Atlas Peak Road, Napa. 707.963.2134. www.deldottovineyards.com.

Eagle & Rose Estate Tours of this small winery are led either by the winery owner or the winemaker himself. Eagle & Rose will customize tours to suit, including lunch if desired. Call for details; by appointment only. 3000 St. Helena Highway North, Napa. 707.965.9463. www.eagleandrose.com.

Fantesca Estate & Winery Set on land that was the dowry gift when Charles Krug marred in 1860, this estate winery specializing in Cabernet features a wine-aging cave built right into the side of Spring Mountain. Open to the public by appointment. 2920 Spring Mountain Road, Napa. 707.968.9229. www.fantesca.com.

Far Niente This winery boasts the first modern-built wine caves in North America. Built in 1980, the cave area now totals 40,000 square feet and is part of the active tours that the winery encourages visitors to take. 1350 Acacia Drive, Napa. Open to the public by appointment. 707.944.2861. www.farniente.com.

Flora Springs Winery and Vineyards Open to the public by appointment, this small, family-owned winery takes visitors on a "VIP" tour through its hillside caves for barrel tastings by appointment. $20. 1978 W. Zinfandel Lane, St. Helena. 707.963.5711. Their tasting room, open to the public daily, is at 677 S. St. Helena Hwy., next to Dean & DeLuca on Highway 29 in St. Helena. www.florasprings.com.

Frazier Host to the Wine Country Film Festival July 26-29 this year, Frazier offers two cave experiences for visitors. A sit-down tasting of four releases is $20; a tour and tasting, complete with cheese and chocolate pairing, is $30 per person. They suggest reserving a week in advance. 70 Rapp Lane, Napa. 707.255.3444. www.frazierwinery.com.

Hall With two tasting rooms, things can get confusing. Hall Wines has an outlet in St. Helena but the wine caves are at the tasting room in Rutherford. Winery co-owner Kathryn Hall is the former U. S. ambassador to Austria and the 14,000 square foot caves show her love for her adopted country, lined as they are with handmade antique bricks, some of which are marked with an H, for the Hapsburg family. 56 Auberge Road, Rutherford. 800.688.4255. www.hallwines.com.

Hartwell Vineyards Open to the public generally Monday-Friday, Hartwell hosts tours of its caves and surroundings Wednesday-Saturday at 11am and 2pm. $45 includes a sit-down tasting in the cave with food and reserve wine pairings. 5795 Silverado Trail, Napa. 707.255.4269. www.hartwellvineyards.com.

Ladera Vineyards Meaning "hillside" or "slope," Ladera's original buildings date back to the 1880s. The winery hosts tours Monday-Saturday that wind through the estate and include the quarter-mile of underground aging cellar still in use. 150 White Cottage Road S., Napa. 707.965.2445. www.laderavineyards.com.

Long Meadow Ranch One of the only local wineries to combine olive oil production with its vinting practices, LMR is also a full-scale sustainable farm raising its own grass-fed beef and selling its produce. The rammed-earth tasting room was made from the dirt displaced when building the wine caves. Tours can be extra lavish, including a chef meal and library reserve wines. 1775 Whitehall Lane, Napa. 707.963.4555. www.longmeadowranch.com.

Miner Family Vineyards This family winery offers a seated private "Grand Cru" tasting, replete with food and wine pairings, in its caves. 7850 Silverado Trail, Napa. 707.944.9500. www.minerwines.com.

Newton Vineyard Newton is open to the public for tours of its property and cave as well as tastings, Thursday-Monday at 11am by appointment only. 2555 Madrona Avenue, Napa. 707.963.9000. www.newtonvineyard.com.

Pine Ridge Winery The "Cabernet Cave" at Pine Ridge is some 130 feet underground and some 300 feet into the hillside. The winery hosts corporate parties in the cave, but for the non-incorporated, a daily barrel-to-bottle Cab tasting is available for $35, including an artisanal cheese pairing. 5901 Silverado Trail, Napa. 707.253.7500. www.pineridgewinery.com.

Quintessa Situated the Rutherford Appellation off the Silverado Trail, Quintessa takes visitors on a short hike through the vineyards before leading them into the underground caves for a sit-down tasting. Tours are at 11am, 12:30pm and 2:30pm and are by appointment. $35. Given the curious restraints of Napa's quaint zoning laws, picnicking is strictly verboten. 1601 Silverado Trail, Napa. 707.967.1601. www.quintessa.com.

Reverie on Diamond Mountain One of the smallest Napa wineries, Reverie is also one of the mightiest, causing the storied French Laundry to bid mightily on a recent lot of Reverie Malbec at auction. For small groups, the by-appointment tours have no charge; rather than sit-down tastings and tours as touted at other places, Reverie prides itself on its "walk-around" tours, which inevitably end with a surprise of great natural beauty. 1520 Diamond Mountain Road, Napa. 707.942.6800. www.reveriewine.com.

Rombauer Vineyards While Rombauer's extensive cave system is mostly a workhorse for aging their wine, staffers will gladly lead a tour of the caves by appointment and at no extra cost. Tasting fee, $10. 3522 Silverado Trail, Napa. 707.963.5170. www.rombauervineyards.com.

Rubicon Estate Rubicon aims to educate and to that end offers a two hour "Elevage Experience" in which visitors learn about winemaking from field to cellar. The tour includes a swing through the caves as well as a barrel tasting and Cabernets with cheese. 1pm daily. $50. 1991 St. Helena Highway, Napa. 707.968.1100. www.rubiconestate.com.

Rudd Now encompassing the Dean & DeLuca gourmet food market in his empire, winery owner Leslie Rudd offers a comprehensive two-hour estate tour that ends with a sit-down tasting pairing Rudd wines with treats prepared by the executive chef at D & D. $60. 500 Oakville Cross Road, Napa. 707.944.8577. www.ruddwines.com.

Rutherford Hill Winery Nearly a mile of tunnels comprise the wine-aging caves at Rutherford. Daily tours at 11:30am, 1:3pm and 3:30pm include tasting and are just $15. 200 Rutherford Hill Road, Napa. 707.963.1871. www.rutherfordhill.com.

Sawyer Cellars Proud that all of their wine is estate-grown, Sawyer uses gravity feed to craft its wines, and dug its library and cellars into the ground under and behind an existing barn that the owners have meticulously preserved. Tours and tastings available Monday-Friday by appointment. $10-$15. 8350 St. Helena Hwy., Napa. 707.963.1980. www.sawyercellars.com.

Schramsberg Vineyards This sparkling-wine mecca boasts the oldest caves in the Napa Valley, hand-dug by Chinese laborers in 1880. Again, due to Napa's curious permitting, Schramsberg tours must be couched in education, which is all the better for the visitor. Four general tours a day are available as well as a special food and wine pairing. July hours are different due to construction. $25-$50. 1400 Schramsberg Road at Peterson Drive, Napa. 707.942.6668. www.schramsberg.com.

Shafer Vineyards Up to 10 visitors are welcomed by appointment daily for a sit-down tasting and tour of the cellar and cave. $35. 6154 Silverado Trail, Napa. 707.944.2877. www.shafervineyards.com.

Spring Mountain Vineyard This 1885 estate is open by appointment only for tours, tastings and a visit to the cellars. $25. 2805 Spring Mountain Road, Napa. 707.967.4188. www.springmountainvineyard.com.

Staglin Family Vineyard Known for its extensive modern art collection and for providing the setting for the remake of The Parent Trap, Staglin is proud that its entire winery is underground in the vast cave system completed this decade. Tours by appointment only. 1570 Bella Oaks Lane, Napa. 707.944.0477. www.staglinfamily.com.

Stag's Leap Wine Cellars With caves some 100 feet underground designed to host parties, Stag's Leap is open to the public daily and offers private tours by appointment. $40. 5766 Silverado Trail, Napa. 707.944.2020. www.cask23.com.

Storybook Mountain Vineyards Caves dug over a century ago by the founding brothers Grimm are open to those who wish to sip Zinfandel. An open house with the winery family is slated in the caves for Sept. 1. 3835 Highway 128, Napa. 707.942.5310. www.storybookwines.com.

Truchard Vineyards Open to the public by appointment only. 3234 Old Sonoma Road, Napa. 707.253.7153. www.truchardvineyards.com.

Viader Vineyards & Winery Tours are by appointment only; closed Sunday. 1120 Deer Park Road, Napa. 707.963.3816. www.viader.com.

Vineyard 29 Tours by appointment lead through Vineyard 29's vast warren of state-of-the-art caves, replete with sensor-detection lighting and music. $50. 2929 St. Helena Highway North, Napa. 707.963.9292. www.vineyard29.com.

Von Strasser Winery Tours and tastings by appointment. 1510 Diamond Mountain Road, Napa. 707.942.0930. www.vonstrasser.com.

Sonoma

Benziger Family Winery The biodynamic vineyard tram tour (read: a tractor hauls a tram) takes visitors through the vineyards and into the caves. $10. 1883 London Ranch Road, Sonoma. 888.490.2739. www.benziger.com.

Bella Vineyards This tiny family winery welcomes visitors to its extensive new cave system, replete with room for entertaining. 9711 West Dry Creek Road, Sonoma. 866.572.3552. www.bellawinery.com.

Favero Vineyards & Winery Tours of the cave are by appointment only. 3939 Lovall Valley Road, Sonoma. 707.935.3939. www.faverovineyards.com.

Gloria Ferrer Champagne Caves Méthode Champenoise revealed; tours daily. 23555 Carneros Hwy. (121), Sonoma. 707.933.1917. www.gloriaferrer.com.

Gundlach Bundschu Winery Boasting the longest wine cave in California, this fun family winery is emphatically open to the public. 2000 Denmark Street, Sonoma. 707.939.3015. www.gunbun.com.

Kunde Estate Winery & Vineyards Guided tours of the caves are available for free without appointment Friday-Sunday. 10155 Sonoma Highway, Sonoma. 707.833.5501. www. kunde.com.

Nicholson Ranch Caves and "great room" for entertaining completed this century. 4200 Napa Road, Sonoma. 707.938.8822. www.nicholsonranch.com.

Robert Young Estate Winery Caves available to host private parties. 4960 Red Winery Road, Sonoma. 707.431.4811. www.ryew.com.

Schug Carneros Estate Winery No fee for tasting. 602 Bonneau Road, Sonoma. 800.966.9365. www.schugwinery.com.

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