The objective of this project is the construction of a multimodal interchange located in the underground of the Plaza Cataluña of Barcelona between the different railway lines, respecting the operation of the current Integrated Tariff System. The project proposes to improve the connection between the L4 lines of RENFE, the L1 and L3 lines of Metro, as well as the Vallés Line of the Generalitat de Catalunya Railways. The main objective of this intervention is to guarantee access to all persons with reduced mobility, as well as to all persons with small children, carts or with the use of wheelchairs or crutches. The current connection between these lines is full of impossible connections due to architectural barriers such as stairs and level changes. The approach of the project proposes the following premises: • Accessible for all, easy to orientate. • Equal distances between lines. • Architecture that responds to the movement of people disconnected from rigid rules and linked to road traffic. • New perception of space. • Surgical intervention in specific points of the square taking full advantage of the pre-existence. • Decongestion of the periphery of the square, concentrating new accesses in the centre. • Visual relation between the previous vestibule and the platforms. All routes pass through the same space. • The displacement of the F.G.C station under the car park SABA allowing a more compact performance. The proposed construction process in 4 stages of execution, (1) extension of the F.G.C line and construction of the perimeter concrete screens. (2) Excavation of the central zone and demolition of the vault of metro line 3. (3) Foundation and partial demolition of the vestibule of RENFE line 1. (4) Construction of the cover slab and redevelopment of the square.