Remember, in GTA San Andreas, in the very first cut scene, we are shown the interior of the Liberty City airport? Francis International Airport. This mod adds this interior to GTA 3. It can be accessed in the missions "Marked man" thanks to a bug due to which the doors do not close after Ray runs inside.
Installation: replace all files from the archive in gta3.img. In the landsw.col file, replace the collision from the archive.