Writer Lindsey Bro has collected 50 saunas, hot springs and baths that represent global bathing culture in the book Thermal. Here, she picks eight of the most intriguing.

Named Thermal: Saunas, Hot Springs & Baths, the book aims to demonstrate the variety of warm spaces that people use to bathe.

"Craving heat and warm spaces is universally human and every continent and culture around the world has some connection to it," Bro told Dezeen.

"I very intentionally wanted to represent the vast experience and rich heritage we all have with saunas, springs, and bathing culture."

The book includes a wide variety of spaces used for bathing including natural hot springs, outdoor baths and architectural saunas from all across the world.

"It's fascinating to think about why humans have always been drawn to warm waters and warm places," explained Bro.

"I wanted to not only understand this sense of connection, but celebrate its diversity, its beauty, and its mystery."

Bro hopes that the choices of spaces in the book, which all have a connection to nature, will generate a feeling of connection.

"There is really nothing more beautiful or true than nature; these spaces all bow, in some way, to the beauty, experience, or awe of our natural world and our place in it," she added.

"I hope readers take away the understanding that we're all connected – to ourselves, our past, nature, one another – and that it's this sense of connection that brings us a true sense of peace and well-being."

Esalen Institute, by Mickey Muennig, California, USA

"Perched on the cliffside, overlooking the Pacific Ocean, at the heart of American mysticism, the original 1960s Esalen baths were redesigned by Mickey Muennig in the 1990s.

"Here, the intention is to touch the sublime, allowing guests to experience profound transformation through self-work, retreat, study, and a surrender to the natural environment. The baths at Esalen represent a meeting of three waters – where fresh, sweet water from the mountains meets the hot springs, which then meets the wild Pacific."

Grotto Sauna, by Partisans, Georgian Bay, Canada

"Sculptural, sensual, and designed in conversation with nature, The Grotto sauna, located in Georgian Bay, Canada, is arresting and still.

"Nestled on the cliffs edge, Partisans architecture studio designed the space as a sanctum and refuge from the harsh, often battering weather of the exposed bay."

Sauna Ranco, Panorama Arquitectos, Chile

"Designed by Panorama Arquitectos in Chile, Sauna Ranco plays with pattern and form to create a sense of poetry and solitude, echoing the experience of the surrounding raw and intense landscape.

"With three rooms connected by a continuous walkway, each space is carefully positioned away from one another, creating a sense of framing and refuge."

Goodland Tubs, by Goodland, Canada

"It's hard to innovate a tub, but Goodland did.

"Pulling on elements of nature, solitude, meditation, process, and innovation, they were able to simplify and transform a wood-fired hot tub from somewhat burdensome – but beautiful – to a sleek, minimalist design with efficiency and interaction — with both nature and one's self — at the forefront."

The Bands, by Oslo School of Architecture and Design, Lofoten Islands, Norway

"Located in the Lofoten Islands, in the Arctic Circle, this (essentially) art project by students of Oslo's Scarcity and Creativity Studio from the Oso School of Architecture and Design is an incredible example of how sauna is really about community.

"Designed to mimic the surrounding landscape while using sustainable solutions and resources, this project is as stunning as it is thoughtful."

Felsentherme, by Gerhard Garstenauer, Bad Gastein, Austria

"Nestled in the high Austrian Alps, Bad Gastein sits looking like a village designed by Wes Anderson. Wild a deep, rich, and storied traditional of thermic bathing and healing waters, Bad Gastein is known as home to the romantics and dreamers of days gone by.

"Here, vintage la belle epoque charm oozes out of every opulent, grand hotel and people walk the streets clad in bathrobes, walking from one bath to another."

Cré Natural Building by Bryce Ehrecke and Kelly Brown, Joshua Tree National Park, USA 

"Designed to connect people to place, Bryce Ehrecke and Kelly Brown of Cré Natural Building use natural building techniques to craft meaningful spaces and natural aesthetics. Build in consideration of the environment, surrounding flora and fauna, and those who will interact with what is being built, no two structures are ever the same, embodying a fleeting and ephemeral aesthetic in service to the surrounding environment.

"Here, this natural tub is built in the high desert, reflecting the native colour palette, resources, and materials available."

Project Ö, by Aleksi Hautamaki and Milla Selkimaki, Archipelago National Park, Finland

"Located in the far north of Finland, this remote island is a love letter to the world around. One part experiment, one part presence, and one part intentional design, Project Ö, which translates to island, is designed to echo the traditional aesthetics of the region while taking up as little space as possible.

"Being in such a direct relationship with nature, it's no wonder owners Aleksi Hautamäki and Milla Selkimäki used Project Ö as an excuse to design solutions for more intentional, low-impact living. Like using heat from the sauna to warm the property's water and floors."