The 180-meter-long underpass is located 8.5 meters below the station level. Escalators and elevators lead from the platforms to the tunnel. Murals totaling 550 square meters have also been painted on the walls, depicting the history of Polish railways and Warsaw. This newly created mural is the fourth of its kind completed by PORR as part of its railway investment projects. It follows murals created as part of the modernization of the E30 railway line, the LK131 LOT A Chorzów Batory–Nakło Śląskie line, and the LK93 Oświęcim–Czechowice-Dziedzice line.

The modernization of Warszawa Gdańska station also included a comprehensive reconstruction of the platforms. New surfaces were constructed, along with elevators, escalators, and canopies. The station was also equipped with a modern passenger information system, CCTV, and a new sound system. New tunnel entrances were constructed from Słomińskiego and Ks. Romana Indrzejczyka Streets, and access to the platforms was provided by both stairs and elevators.