The Coruscant subway was a system of underground railways on Coruscant.
During the Battle of Coruscant in 19 BBY, General Grievous and some IG-100 MagnaGuards chased Supreme Chancellor Palpatine and Jedi Shaak Ti, Roron Corobb, and Foul Moudama through the subways in an attempt to kidnap the Supreme Chancellor. The ensuing pursuit damaged the subway's automated turnstile, a window, and possibly a train when a MagnaGuard droid was thrown in front of it. After the Jedi destroyed the MagnaGuards, Shaak Ti managed to defeat Grievous by using the Force to tie his cape to a train and activate it, whisking the general away.
Shortly after the pursuit, the Jedi and Palpatine met with Jedi Masters Mace Windu and Kit Fisto, who boarded a train to get to Palpatine's bunker. On the way there, Grievous, along with several battle droids reappeared and attacked the Jedi, forcing Windu to duel the cyborg on top of the train.
At this time, entrance to the subway cost each passenger two Republic credits.