Recycled shipping containers have graduated from the experimental stage and are now regularly upcycled as homes, multi-unit housing, in-ground pools, and art galleries, which use the plentiful and sturdy boxes for their core structures. But in San Francisco, Soak, an urban bathhouse and prototype pop-up business, is taking the concept a step further—and greener.

The personal services sector typically uses a lot of water and energy, but Soak instead combines photovoltaics, solar hot water, and filtered rainwater to operate its sauna, solarium, hot pools, and showers completely off the grid. Call it eco-hedonism.

Designed by Rebar (which recently became two separate entities: Gehl Studio, the San Francisco office of Denmark’s Gehl Architects, and the independent MoreLab), the spa also can relocate much like a mobile home (though in decidedly higher-rent surroundings), allowing Soak to serve clients throughout the Bay Area without building new locations.

Check out more renderings below.

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