The concept of tunnels first surfaced after an internal file search, soon after the release of the game and was later cemented years after, disclosing a couple of signs relating to Panlantic tunnels and tunnel testers. Post-discovery, players began to modify the game and deliberately included tunnels in the game. It was further revealed that these files belonged to the Panlantic Construction Company and Avery Carrington. For this reason, Avery Towers are assumed to be the accurate location of these tunnels. These tunnels were later removed by Rockstar prior to the final release for undisclosed reasons. The textures in question are located inside the tunnels.txd texture grouping. There are three textures here, tunnel_128, a sign warning about road closures and tunnel testing, panlantic_128, the logo of the Panlantic Construction company, and corugwall1128, which appears to be a container or retaining wall used in construction projects. These textures appear to be a leftover from GTA III, a game that has a functional tunnel system. In the blockade near the collapsed Cedar Grove tunnel, the tunnel testers sign can be spotted.
Although, the core location is definite to be Avery Towers, but players have examined that these tunnels were to be spread all over the eastern part of the city i.e. Vice Point, Washington Beach, and Ocean Beach. While others have related these tunnel paths to the Gator Keys. However, these paths are rather too vague and would occupy one-fourth of the city.
A thesis interlinked with Funeraria Romero loomed a decade after the game's release. This theory was formed on the basis of a manhole and basement door found alongside/under both the Riverside Pavillion shops. Mainly due to the vague association between Romero's and Riverside Pavillion because of their respective locations, parallel to each other. Therefore, the theory states that there's in fact a passage between the manhole and the basement. Players have alleged that this tunnel passage was effectuated to transport certain victims abducted by the Romero's. Even though, this theory isn't yet confirmed by Rockstar but still holds a strong ground on its own.