ROSAT 0.75 keV surface brightness map around the Galactic center. Five selected bright regions (red) are labeled and shown. The central parts of those regions correspond to the five LOS drawn in the four meridional cuts in Fig. 6 and the top-right of Fig. 7, allowing to correlate visually the bright X-ray sources (hot ISM) and low density regions or tunnels appearing in the 3D maps.