The Fortnite: Battle Royale map has undergone some changes following the recent V.4.4 update, which has spawned some speculation among fans.
Over the course of Season 4 in Fortnite: Battle Royale, a collection of changes and adjustments have been made to the map by Epic Games to further the 'storyline' since its release.
After the map was struck by various meteorites at the beginning of Season 4, various 'renovations' and 'clean up efforts' have been implemented by Epic Games over the course of multiple updates by trucks that carry debris out of a certain area.
While many fans claim that the underground region may just be a glitch in the map, others believe it could be a 'bunker' or 'tunnel system' that will protect against the theorized launch of the rocket found by Snobby Shores.
A better look at the Greasy Grove underground area can be viewed below.
As of writing, everything is just speculation, with no official word being released by Epic Games regarding future plans for Season 4.