The towering fortress of fairy tale character Rapunzel inspired this steel-clad house extension that accommodates the three oldest daughters of Austrian architect Stefan Marte (+ slideshow).

Named Maiden Tower, the four-storey residence sits alongside the family's existing concrete home in the Alpine district of Vorarlberg, western Austria, and is clad with oxidising steel to create a visible contrast between the new and old structures.

Stefan Marte, of Marte.Marte Architects, planned the building over four storeys, allowing each daughter to have her bedroom on a different floor to her sisters.

A corridor leads through to the extension from the existing house, arriving at a small library. Beyond this, the girls have their own separate kitchen and dining room.

A corner staircase leads up to the bedrooms, while doors lead out to a swimming pool and terrace in the garden.

Corten-steel panels clad three sides of the tower, while the east elevation features floor-to-ceiling glazing, offering views back towards the main house.

Additional windows and doors are dotted across the north and south elevations and can be concealed behind hinged steel shutters.

This is the third project by Marte.Marte Architects to feature on Dezeen recently, following a twisted bridge and a concrete holiday house.

See more architecture by Marte.Marte Architects »
See more houses in Austria »

Photography is by Marc Lins.

Here's a project description from writer Marina Hämmerle:

Maiden Tower

What could match the massive presence of Marte's concrete home, this raw, stony material, this self‐contained unit? Oxidising steel: just as raw, just as authentic in its expression and its properties. The interior impression remains the same – wood surfaces, warm colours, fine pores. The new exterior structure, on the other hand, is masculine, striving skywards, rising up from the surrounding landscape like the neighbouring pear tree. That behind the massive exterior lies a building of lightweight materials may be inspired by the tale of the Trojan horse.

A new space opens up between the two buildings, complemented by an in‐ground pool – uncompromising, hard, less sensible, but therefore all the more magical, idiosyncratic, and sensuous. Oxidising steel on the walls and bottom, encased like in a suit of armour. The tower also appears this way with its steel ventilation flaps to the north and south and fixed glazing to the east.

Rapunzel, Rapunzel... Through the library, down a few steps into the separate kitchen, and then through the dining room, facing the pool, the little princesses can climb the newel stairs to their bedrooms. There, they are presented with a view, on the one hand, of their parents' protective house and, on the other, the nearby scenic forest. The spatial perspective mirrors this interplay of freedom and guidance, becoming a symbol of their possibilities for development within the family.

The whole structure seems so sealed off, but in terms of use, it not only offers an astonishing amount of free space, but also conveys respect and draws boundaries. This makes it possible to live together in a relatively small space and at the same time provides each person with opportunities for participation and private space.

What an unparalleled atmosphere for the girls. If it is true that the first few years of life shape our future spatial desires, then these girls will have had a very valuable personal experience that their future Prince Charmings will probably not have had: a life in manifest appreciation.