: Players could fly between cities or use a revamped airplane ticket system at airports.

GTA: Underground was more than just a map extension; it was a total conversion that integrated the assets and mechanics of several classic titles into the San Andreas engine.

: The mod added Liberty City (GTA III), Vice City (GTA: VC), Carcer City (Manhunt), Cottonmouth (Manhunt 2), and Bullworth (Bully).

: You could buy businesses and safehouses across all maps, with some properties generating passive income.

: A custom fork of SA-MP allowed players to explore this massive combined world together online. The Project's Shutdown

In September 2021, the lead developers announced the end of the project. How To Install GTA Underground for GTA SA