Called Three Square House, the house in Southern Savonia is made up of three interlocking volumes, with a central building flanked by two smaller spaces.
These auxiliary rooms house a garage, storage and a sauna.
Between the garage and the main house a corner of raised wooden decking with a sunken tub connects to a walkway down to a jetty out into the lake.
Facing the line of spruce trees, smaller openings create darker spaces that are intended to evoke the atmosphere of the forest.
Facades facing the lake are more open, with large areas of glazing that wrap around living spaces.
Following a gentle slope on the site, Three Square House sits dug-in towards the forest and slightly raised where it overlooks the water.
Rooms follow these gradients, with private and darker bedrooms at the back and lighter communal spaces at the front.
Instead of doors, sliding glass doors can separate or open up the rooms.
The main building is split diagonally by a central core, maximising the available space in the triangular areas either side.
Enclosed by dark-wood lined walls, this core contains a bathroom, walk-in wardrobe and storage
The core's perimeter houses a wall of kitchen appliances and cabinets.
A triangular living space, defined by this kitchen wall and a corner section of glazing, has a wood-burning stove suspended just above the floor.
Dark wood floors and black ceilings also contribute to the feeling of intimate, shadow-filled spaces.
In the sauna paler wood has been used, along with high-level windows that allow light in while maintaining privacy.
"The design of the building's spaces is not afraid of darkness but has turned it into a strength," said Studio Puisto.
"The building has places with a huge amount of light and places where you can curl up into the shadows, always according to the situation and mood."
Previous projects by Helsinki-based Studio Puitso include a neighbourhood sauna located in a former industrial building, and a home in the Netherlands clad in blackened timber.
Photography and video is by Marc Goodwin.
Architects: Studio Puisto Architects
Partners: Mikko Jakonen, Emma Johansson, Sampsa Palva, Heikki Riitahuhta, Willem van Bolderen
Team members: Pauliina Kujala
Lighting design: Lighting Design Collective
Contractor: Rakennuspalvelu Ri-Li Oy
Roof and facade zinc work: Peltipeite
Walnut surfaces and fixed furniture: TM Team KY