The Blue Lagoon was an accidental discovery. Lore has it that, in the 1970s, a worker from a geothermal plant was suffering from psoriasis and decided to take a dip in the super-warm waters, a byproduct of the plant. Immediately his skin felt better, and soon others were taking the plunge. By 2005, the Blue Lagoon Clinic and Spa opened at the site, designed by architect Sigríður Sigþórsdóttir. Fast-forward to present day, and 2,500 people visit daily, making the Blue Lagoon one of Iceland’s most popular tourist attractions. And it’s about to get even bigger—Sigþórsdóttir’s firm, BASALT Architects, in collaboration with Design Group Italia, is hard at work on the site, readying it for the next phase—a new five-star hotel with 60 rooms, slated to open in 2017. Here, the architect shares background on the unique challenges of a most unusual site.

The Blue Lagoon Clinic and Spa served as a prototype for the new hotel. What’s the connection?

Sigríður Sigþórsdóttir: The first project features prefabricated lava-coated elements—the real lava from the site was used as the finishing layer. That had not been done earlier in Iceland, and I really wanted to make the building grow up from the lava field in a clear, man-made way. We are using crushed lava instead of imported marble stones in the finishing layer, as is usually the case in Iceland. The new hotel has a number of different concrete finishes that are achieved by using prefabricated elements, manufactured under the best possible circumstances. This enables us to get large, smooth surfaces that are uninterrupted by joints.

Your team laid out lines as to where the lava stone would be cut, and then adapted to the landscape by raising the building by roughly 16 inches. Part of the building will now sit approximately 23 feet below ground. What influenced this decision?

Sigþórsdóttir: Such a place imposes strict limitations on the onsite production; great care has to be taken towards the unique environment. This has been done in all the Blue Lagoon projects. In fact, a tight line was laid out around the footprint of the buildings and strict penalties imposed should anyone cross it. Offsite construction, such as the prefab elements, lightened the impact on the site. The natural surface lava formations played a big role in the initial layout of the building. During and after the earthwork, the plan must be adjusted to natural crevasses.

Describe the process of “cutting” through lava stone.

Sigþórsdóttir: The first thing is to carefully reserve the surface lava stone and store it for later use; this is mostly done by small machines and by hand. Then, more traditional earthwork methods take over. A close eye is kept on the heavy machinery and, should they reveal interesting natural formations, the work is stopped and we evaluate whether the design should accommodate the discovery, as is often the case.