This proposal, for a substantial extension to the Serlachius Museum in Gösta, Finland, seeks to respect the origins of the institution. Derived from a private collection, the current home of the museum is a large existing house. It is the centrepiece of its estate, commanding the highest point of an island site, from which the topography falls away through gardens towards the surrounding lake. Our proposal maintains these hierarchies, with the existing house continuing to be understood as the dominant structure, despite the much greater volume of the proposed extension. This is situated immediately to the West of the house within existing trees. The two buildings are physically connected and in close proximity, both for functional clarity and so that they can be understood as complementary parts of a harmonious ensemble, rather than competing elements. Hidden within the trees the low lying extension has minimal impact on the character of the existing building but creates a coherent and elegant sequence of internal gallery spaces that range in scale up to 600m2 and 9m high. It also provides entrance, café, art handling and administrative functions. Its most prominent features are a series of roof lights, which shift in scale, from singular pitched forms that echo and rhyme with the roof of the existing house, to a field of north lights over the large temporary gallery that lies, cut in against the water.