The flat is set inside a 1970s residential block and belongs to a young woman who, after living abroad for a few years, wanted to settle back in her home city of Bilbao.
Locally based studio Azab was tasked with refreshing the flat's interiors before the owner moved in with her best friend.
Working with a very tight budget, the studio could make few structural changes to the apartment – the bathrooms were simply moved closer to the sleeping quarters so that the kitchen could be better connected to the sitting room.
Colour was instead used to define different areas of the flat. The pitched-roof corridor that runs through the centre of the floor plan has been painted bubblegum-pink, and matching carpet has been applied to the floor.
"The use of colour is limited but intense," Iñigo Berasategui, principal architect at the studio, told Dezeen.
"The pink that we used in this project was chosen for its ability to bathe the space with an aura of ingenuity and optimism that is very necessary in a home without many attributes."
The corridor is fronted by a gabled door frame that looks through to the kitchen.
Timber-framed cabinetry here has been preserved, but refit with forest-green panelling. Mint-green tiles have also been used to form a splashback behind the sink and clad the floor.
Flashes of colour have been more subtly introduced at other points in the interior. For example, the inner lining of a full-height bookshelf has been painted cherry red, and a turquoise glass pendant lamp has been suspended from the ceiling.
All other existing decor details, like the skirting boards, mouldings and storage units, have been left in their found state.
"[The flat] is an exercise in archaeology that aims to grab the intervention with the value of the original elements of carpentry," added the studio.
Azab was established in 2018 by Cristina Acha, Miguel Zaballa, Ane Arce and Iñigo Berasategui.
The studio isn't a stranger to using colour in its projects – earlier this year it used pale-blue curtains to divide living spaces inside a family home, and added a baby pink kitchen to a 1960s flat. Back in 2019, it also introduced sunshine-yellow walls to a formerly characterless attic apartment.
Photography is by Luis Diaz Diaz.