Elden Ring dataminer Sekiro Dubi has dug further into those massive, inaccessible arenas dotted throughout the Lands Between first highlighted by fellow Souls hacker Lance McDonald. Sekiro Dubi restored a Site of Grace and some enemies slated for the areas, shedding more light on their intended use.
In Lance's original video, he passed through the locked entrance of the Limgrave arena with a free cam tool to take a look inside, revealing extensive seating, a sand pit for combat, and opposing elevators leading into the coliseum's underbelly.
Sekiro Dubi dug into files related to the "Leyndell Colosseum," reimplementing its interior for normal gameplay alongside an unused Site of Grace. The entryway to the coliseum is lit by torches, and features an altar with some kind of fossil-like rock formation on top.
Sekiro Dubi also showed the arena proper, where a Lion Guardian (one of those knife lions from Redmane or Castle Sol) does battle with a Grave Warden, a gladiator-like enemy found outside the Leyndell arena and as a boss in various catacombs throughout the world.
It's still unclear what purpose these arenas were meant to serve. Much of the speculation has focused on their potential as PvP arenas similar to the ones from Dark Souls: Artorias of the Abyss or Dark Souls 3's Ashes of Ariandel. Given that they featured NPC opponents at some point, I could also see them being used for a boss rush mode like the one from Sekiro.
Sekiro Dubi points out that the Ritual Shield Talisman's item description makes note of arena combat occurring in the setting's past, potentially indicating that these arenas could feature in a time travel sequence like the Artorias of the Abyss or Ringed City DLCs.
Hopefully we won't have to wait too long to see whether or not the arenas factor into FromSoft's future plans for Elden Ring.