The final part of the jigsaw consists of a range of four currently empty upper galleries on the eastern side of the rambling building complex. These used to be part of the adjoining National Portrait Gallery, but were handed over in the late 1990s in a property swap which allowed the NPG to build its Ondaatje Wing. They have stayed empty because their floor levels are higher than the National Gallery's, so making it difficult to knock through. In the Dixon and Jones masterplan, the floors will be lowered and a new semicircular staircase inserted to link the levels at the eastern end.