WARNING: The following contains major spoilers for Infinity Wars: Sleepwalker #2 by Chad Bowers, Chris Sims and Todd Nauck, on sale now.
Marvel Comics' latest major event, Infinity Wars, is centered around six of the most powerful artifacts in the Marvel Universe -- the Infinity Stones. It's common knowledge at this point that anyone who wields an Infinity Stone more or less has complete control over one aspect of creation: Mind, Soul, Space, Power, Time or Reality. Beyond that, the stones are fairly mysterious, the means by which they operate left open to the imagination of the reader. That is, except for the original stone, the Soul Stone, which has long been considered the most complex of the ancient artifacts, if only because it contains an entire pocket dimension within it.
Infinity Wars: Sleepwalker #2 reveals that the Soul Stone is no longer unique in that regard. In fact, the series looks poised to explore each stone in-depth, starting with the Power Stone. The issue reveals that, while the Soul Stone lays claim to the formerly utopic Soul World, another pocket dimension akin to Soul World exists inside the Power Stone -- the Arena. The Mindscape cop Sleepwalker must traverse this dangerous (and muscly) realm if he is to reunite with his human host from the waking world, Rick Sheridan.
That's a lot to digest, though, so let's take this one a little easy and start from the beginning. First appearing in Marvel Premier #1 by Roy Thomas and Gil Kane in 1972, the Soul Stone (originally called the Soul Gem) was introduced solo, gifted to Adam Warlock by the High Evolutionary, who tasked the newly-reborn hero with sorting out Counter-Earth's Man-Beast problem. The gem stayed with Warlock for a time, until he realized it had a penchant for eating souls. Eventually, the stone even spoke to him and, in time, ate him up, too.
Infinity Wars has revealed the inside of the Soul Stone to be a pretty sucky place, all full of whipping winds, ethereal deserts and one really, really big tentacled monster named Devondra that just wants to chow down on anything it can wrap itself around. That hasn't always been the case, though. Soul World was once an idyllic, quiet place, free from the violence, stress and anger that defines earthly life. Infinity Wars and the various comics leading up to it established that the stone was corrupted, leading to the chaos seen on the page and the present predicament where Gamora has folded the universe over on itself.
The remaining five stones (and a seventh -- the Ego Stone -- that has been all but lost to time) were introduced later, but their powers, as mighty as they may be, never quite reached the heights of the Soul Stone. The Power Stone let its users smash their enemies into little, tiny bits if they so pleased, but there was no Soul World equivalent. Now, though, that's no longer the case. Infinity Wars: Sleepwalker #2 has introduced the Arena, and it turns out the dimension within the Power Stone has its own society the hero must contend with. Sleepwalker even gets the honor of negotiating with that society's leader.
The negotiations, of course, go very poorly.