The following contains spoilers for Hulk vs. Thor: Banner of War Alpha, now on sale from Marvel Comics.
Given the destructive potential of both Thor and the Hulk, it makes sense that their latest battle would have to be somewhere special. With both characters having gained notable boosts recently, it was always going to be a destructive bout, and they are now in the perfect setting for such a conflict.
Thor and Hulk's brawl in Hulk vs. Thor: Banner of War Alpha (by Donny Cates, Martin Coccolo, Matt Wilson, and VC's Joe Sabino) is revealed to take place in a fighting arena constructed within the remains of a Celestial -- which is a great idea to add to the Marvel Universe and gives it a spiritual connection to one of the Marvel Cinematic Universe's most memorable settings.
Hulk and Thor are two of Marvel's biggest powerhouses, so any battle between the two is going to take on a particularly brutal edge. But neither man is in a particularly calm place at the moment -- with Banner's attempts to master "Starship Hulk" only unleashing further inner darkness, and Thor's trials as King of Asgard including recently burying his father Odin (only for his spirit to live on in the reforged Mjolnir). Both are in search of a good fight, and end up taking the other's relative lack of limits as an excuse to fully commit to battling one another.
As soon as their brawl begins, Thor notes that they need to be able to carry out this duel somewhere where civilians won't be caught in the ensuing chaos. Calling upon Sif and her control of the Bifrost Bridge, Thor is able to force the battle into one of the galaxy's most unique arenas: the Black Hand of God. As revealed by the Watcher (who has come to witness the duel) the location is actually the severed hand of a Celestial converted into a space station. Chained between the five fingers of that connect to a planet-sized palm is a massive arena that serves as home to some of the most grisly tournaments in the Marvel Universe.
The Black Hand of God serves as something of a counterpoint to other Marvel landmarks, perhaps most notably Knowhere. A major cosmic location that was introduced to the MCU in the first Guardians of the Galaxy film, Knowhere is an important station and largely lawless setting that's composed of the severed head of a long-dead Celestial. Like the Black Hand, it was converted into an important universal waystation. It's even possible that the two locations are connected, and actually come from the same long-dead cosmic gardner. While Knowhere was destroyed in Guardians of the Galaxy, it isn't the only place in the universe where a Celestial's body has been converted into a structure, with even the Avengers converting a deceased Celestial into their current headquarters, Avengers Mountain.
This is a great concept given the general importance of the Celestials, and it effectively gives the Marvel Universe a perfect arena setting that can be used for future stories. It could even be used as a reason to bring the Eternals back into the cosmos, as their fury over the Avengers turning a Celestial into their base could translate to the powerful beings trying to end the desecration of their gods. The Black Hand is a worthwhile addition to the Marvel Universe, effectively giving the heroes and villains their own War World to compete within -- and the perfect place for a throwdown of Thor and the Hulk's magnitude.