The interior consists of a kind of box containing closed and open spaces and covered in a sculptural skin made up of about 4,000 narrow wooden planks. This slatted skin ensures visual privacy by blocking views into the building, but does not obstruct views from indoors onto the sea. Sheltered outside spaces have also been inserted between the cool outer skin and the warm mass of the building.
The building consists of two parts: public saunas and a restaurant. The more private rooms are concealed in opaque boxes while the main spaces have a glazed front for views out onto the sea. The stepped outer skin forms a stairway for climbing to the rooftop viewing platform, thus providing a further place for whiling away time at the sauna. Various degrees of light characterise the building, with daylight in the outer sections giving way to deliberately dimly lit areas, followed in turn by darker and more private sauna areas for enabling visitors to relax and come to rest. Due to its siting, the volume juts out above the water like a landing stage, meaning visitors can hear the sound of lapping waves. In the process they can use the seawater pool whenever they like, both in summer and winter, as well as the cold water basin and fireplace room in the spa area.
The main materials – consisting of black concrete, blackened steel and birch and spruce – are durable and long-lasting, meaning the outer skin will turn grey over time. As a result the building will age naturally until one day it comes to resemble a rock on the seashore, metaphorically speaking. The other materials, namely pressed and glued wood from responsibly managed forests, contribute to the sustainable and eco-friendly character of the facility, along with use of heating from water and wind power and district heating. Even the sustainably caught fish sold in the restaurant fits in with this concept. Certain details, such as the alignment of interior furnishings, demonstrate sensitivity towards human needs. This can be seen in the raised platform that not only divides the main space into two different areas but also provides guests the comfortable feeling of sitting with their backs against a wall.
Löyly is the Finnish word for the steam that rises up when water is sprinkled on hot sauna stones. This communal ritual is now performed several times a day at the edge of the peninsula. In order to make the building as public as possible and thus a place where everyone feels welcome, the main concept behind the facility was to create a mixed sauna with sections in which a bathing suit is required. The fact that there are only 5.4 million people in Finland but 3.3 million saunas demonstrates the cultural significance of the communal spots. Avanto Architects' "wooden rock" is one such place where people can relax in a variety of ways.