Ever since humans and animals chanced upon hot water burbling out of the ground, thermal springs have been a source of warmth and wonder. Extraordinary vernacular architecture has surfaced around them, in the form of places of wellbeing and leisure, and also of fantasy and delight. Besides the curative power promised by natural mineral water, hot springs also symbolise the flow of the imagination and the magnetic hold that the liquid has over our minds and senses.
As a self-professed o-furoholic (a delicious Japanese term for a hot-water addict) I’ve visited as many thermal baths as possible. I’ve been known to make a diversion to the Belgian town of Spa on a work trip in order just to see the magnificent Pouhon Pierre-le-Grand, named after Tsar Peter the Great, who helped popularise the resort. I took the slow train around the Wakayama peninsula in Japan to test the sulphurous springs of Yunomine (the name means ‘hot-water mountain’) that erupt into the river. And I’ve soaked in the cerebral atmosphere of Peter Zumthor’s Therme Vals. But one legendary example has eluded me: Termas Geométricas in Chile. I came across photos soon after it was completed in 2009 and was fascinated by the radiant red walkways criss-crossing a deep green ravine. I’ve still not made it there, but I’ve enjoyed it vicariously through long-distance conversations with Germán del Sol, the architect and instigator of this extraordinary project.
Termas Geométricas is in Villarrica National Park, south of Santiago. Sited on the Mocha/Villarrica fault, which runs from the Pacific to the Andes, the nature reserve is home to three volcanoes, including the one with which it shares a name. It is also known by its Mapuche name, Rucapillán, meaning ‘great spirit’s house’. In indigenous mythology, spirits that inhabit the earth usually live inside volcanoes. Villarrica is one of Chile’s most active: it last erupted in 2015, when the fireworks lasted for several months. It’s this seismic activity that generates the thermal waters rising out of the ground at up to 85ºC. It was those founts and the Mapuche myths swirling around them that attracted Germán del Sol to the region. He had been dreaming about making a project there when a young architect told him about a farm for sale. The price was beyond his means, but Del Sol managed to negotiate a 25-year lease on the land and set about designing an extraordinary balneary experience. Thus, several years later, Termas Geométricas opened, a finely tuned dialogue between humans and nature, water and the weather. Those luminous orange-red timber walkways follow the winding canyon of the Aihué mountain stream for 500 metres, transporting bathers to 17 steaming pools submerged deep within the lush temperate rainforest.
Between soaks they can cool off under waterfalls. Along the way there are sheds with turf roofs containing bathrooms and changing rooms, as well as occasional shelters where guests can relax around an open fireplace. They can also visit the quincho, a covered space where bread is baked in wood-burning ovens. The baths are lined with local slate and built into the natural walls of the creek, so the nalca (Gunnera tinctoria, or giant rhubarb) and moss are reflected in the glassy surface of the water, which f lows over the pool edge and shrouds them in a cloud of steam perfect for such temperate rainforest plants. Del Sol calls the intense orange red of the walkways ‘Rojo Sendero’, or ‘path red’. He hit on the colour when he caught sight of a piece of plastic protecting some tools on the work site: ‘It’s not quite orange, but it maintains its luminous ability with sun and clouds.’ In devising the layout of the baths, he was inspired by the description of monastery baths in Junichiro Tanizaki’s enchanting essay on Japanese aesthetics, In Praise of Shadows. The novelist relates how these were laid out so that monks walked some distance from their quarters to baths hidden among trees, immersed in water, nature and peace.
At Termas Geométricas, Del Sol has tried to emulate this sense of seclusion by designing a series of smaller pools rather than one large one. In order to muffle the chatter of excited bathers, he amplified the sound of water by widening the slow-flowing stream and filling it with small stones. The beauty is that all this appears effortless, but the construction was complex. Del Sol’s first step was to work with geologists to locate the thermal water sources – a process demanding all the delicacy of an archaeological dig, as heavy machinery can disturb the bedrock and displace the springs. It took a team of 40 two years to clean this 600-metre stretch of the creek, using thermometers to take the temperature of the ground before they gently scraped away the natural debris of sand, rocks and logs to reveal 60 sources between 65ºC and 85ºC. Del Sol designed a gravity-fed system to transport the hot water via wooden channels, inspired by those used in local Mapuche mills, to the pools, which are kept at a constant temperature of 39ºC to 41ºC.
Ultimately it is this contrast between man and nature, the precision and the wildness that defines this place and inspired its name. In the words of the blurb, ‘Termas Geométricas allows you to experience the primitive seduction of purifying yourself with water or by lighting a fire, and to let yourself be carried away by its constant movement that retains and calms. The architecture allows you to be carefree and enjoy the pleasure of bathing or watching, just for the sake of it. Geometry highlights what is natural, and separates it from what is built’.
Visit termasgeometricas.cl
A version of this article appears in the February 2024 issue of The World of Interiors. Learn about our subscription offers
