Providing structural solutions to complex challenges below ground has become a speciality of the house. Fitting a modernist nineteenth-century market in the heart of Barcelona with a single post-tensioned concrete slab, 1 metre thick, resting on a 20 x 20 m square opens up an infinite range of opportunities for the project, such as excavating four basements below the water table and integrating such valuable archaeological remains as the medieval counter-escarpment or a former Roman road, integrating them naturally into the final project. Running a road tunnel beneath four of Barcelona’s main rail tunnels, three of them with no floor slab or counter-vault, 30 metres deep and below the water table, using pioneering, revolutionary building techniques, opens up many opportunities for challenges that theoretically are unsolvable. Our multidisciplinary approach to projects, in which no discipline is prioritised over any other, enables solutions to be found from structural engineering to challenges that would usually only be tackled with land engineering. This way of working has enabled us in recent years to be involved in such major projects as the Glorias tunnels in Barcelona, the burial of the A-5 in Madrid, and the burial of the Malaga sea front.