We describe a deep multi-colour NIR survey (TCS-CAIN) that has been recently completed at the Instituto de Astrofísica de Canarias (Spain). The survey is of selected areas distributed along the Galactic plane and it goes deeper than 2MASS or DENIS. Its aim was to explore the large-scale structure of the Milky Way and the Galactic components, in particular the Galactic bar. This survey has ~10 million point-source detections in J, H, and Ks filters with a photometric accuracy of ~0.1 mag in the three bands and a positional accuracy of ~0.2´´ (based on the 2MASS catalogue as the astrometric reference). Approximately 530 fields have been observed in near plane regions of the Galaxy covering a total area of ~41 deg2 in the sky. This survey is at least one magnitude deeper than 2MASS, and even more in the inner Galaxy where it is less limited by source confusion.