Five super-scenic hot springs

California’s hidden Zen soaking destination

Calistoga, Orr, Beverly, Desert: they’re the California hot springs you may already know about. One you probably don’t (and I’ll be the target of some serious ire back home for spilling the beans about it here) is Tassajara, hidden deep in the Los Padres National Forest, inland from Big Sur. Affiliated with the San Francisco Zen Center, Tassajara is reached via a 14-mile dirt road and for much of the year functions as a retreat so is closed to day visitors. But from late April to mid September, from 9am to 9pm, those willing to make the trip can avail themselves of burbling springs that were used by the indigenous Esselen people for centuries before California was even a territory of Mexico, much less a US state.

The experience is organised into men’s and women’s open-air bathhouses, both of which border a cool creek you can hop into after a warm soak. There’s no WiFi or cell service; but there are meditation sessions, hiking trails, and delicious vegetarian food in the canteen. The stars that come out after sunset are reason alone to make the trip.

STAY: if you’re not doing a full Tassajara retreat (they start at three days), your best base is Carmel Valley; for a splurge, the lush Bernardus Lodge is Monterey-colonial pretty. In Carmel-by-the-Sea, the Cypress Inn, long owned by the late Doris Day, is a stalwart; many of the cosy rooms have fireplaces and there’s a sweet courtyard restaurant. sfzc.org, retreat fees from about $288; day pass $35. bernarduslodge.com, from about $435. cypress-inn.com, from $279

Semi-secret thermal bliss in Tuscany

Italy boasts some of Europe’s finest thermal waters and spas, with Tuscany’s Saturnia and Fonteverde, both of which have dedicated (and swanky) resorts, leading the way. Less familiar to foreign tourists – and quite a bit wilder and, bonus, completely open to the public – are the Bagni San Filippo, in the tiny town of the same name (population: around 100), and the Terme di Petriolo. At the former, a cascade of sulphuric waters with a preponderance of calcium carbonate deposits delivers on both therapeutic benefits and photo-ready scenery: the sulphur eases muscles, while the calcium carbonate has formed limestone deposits in fantastic shapes.

The latter (just off the Siena-Grosseto highway, so super-easy to reach) has hydrogen sulphide-rich, hyperthermal water that sits at about 43C, and large, shallow natural pools. And historic cred: good enough for Gonzagas and Medicis, good enough for us. Come early in the morning or at twilight for maximum atmosphere, and fewer crowds.

STAY: Charlotte Horton and Alexander Greene’s Castello di Potentino is a winery-agriturismo-cultural events venue that’s unique in southern Tuscany. The eight rooms are outrageously atmospheric, with antique beds and tapestries and hand-painted ceilings. For families, the stylish Podere Sant’Adele, just outside the town of Cetona, sleeps 10 with a lovely pool and its own vegetable garden. potentino.com, rooms from €180. Podere Sant’Adele, from €7,830 a week, through merrioncharles.com

High desert and soothing waters in Chile

They’re 19 miles from the town of San Pedro de Atacama, and almost 11,400ft above sea level. The bracing altitude and wilderness surroundings only enhance the appeal of this handful of connected pools, whose crystalline mineral thermal waters average between 25ºC and 30ºC, ranging cooler as the pools descend, some connected by waterfalls that double as natural hydromassage facilities.

There are various lounging platforms and stepped walkways that lead into and out of prime soaking areas, and simple changing facilities on site (but no café or shop, so bring plenty of your own water). Lush greenery and strands of blonde pampas grass and bulrushes are interspersed with massive boulders, and jagged red peaks frame a deep blue desert sky.

STAY: Noi Casa Atacama in San Pedro has contemporary rooms set around a pool and solid sustainable-design bona fides. noihotels.com, from €262

Plunge into Iceland’s “Steam Valley”

The Blue Lagoon may be one of the most famous hot springs in the geothermal powerhouse that is Iceland (and the one that boasts the fanciest accommodation); but Reykjadalur, in the country’s south, gives it a run for its money. The name translates as “Steam Valley”, and the healing waters here take the form of an actual river (thermal pools and mud baths abound as well, but they’re far too hot to bathe in – keep an eye on the signed temperatures as you go). It’s a 3km walk to reach the therapeutic parts, but the payoff is a magical landscape: verdant slopes skirted in drifts of lacy steam, streaked with livid sulphur, dotted with silver-blue thermal pools. The further up the river you go, the hotter the water.

A few wooden walkways have been added, and here and there are deeper lagoons, indicated by rock walls, which make for nice immersion points. And the long, long summer days here mean that come June, a midnight soak isn’t out of the question.

STAY: the Ion Adventure Hotel complements the region’s thermal pleasures with a portfolio of super-alpha adventures, from snowmobiling on glaciers to snorkelling between tectonic plates in Thingvellir National Park. The design skews a bit severe, but you’ll be looking out the floor-to-ceiling windows most of the time anyway. ioniceland.is, from about £295

@mariashollenbarger