Of course, every celestial knows that; the Eden Experiment was a major factor in both the Rebellion and the opening of the Gates of Hell, after all. The names of Haniel and Jophiel, its angelic guards, aren't as common knowledge, but the fact that it exists on Earth isn't hard to learn. Though it's not quite accurate.
Somewhere in the deserts of the Middle East is a tiny oasis, a perfect disc of green grass, tall trees, and clear blue water. It's near-impossible to find on purpose without supernatural aid, but wandering in by accident isn't unheard of. There's always at least one other creature there, too: usually a bird or lizard and never a snake. This is Haniel or Jophiel, at the gates of Eden, and if you close your eyes and drink the oasis waters, when you open them again, you will be within the Garden.
Eden was once a perfectly ordinary corporeal garden, albeit one divinely crafted and tended. Perhaps it's that link to the divine that changed it into what it is now: a strange corporeal-celestial gestalt, where living bodies and soul-shapes can walk side-by-side, where the supernatural and unnatural make no disturbance, and where stray Tethers flicker in and out of existance according to the ebbs and flows of human belief.
Whichever of Haniel or Jophiel is not currently guarding the oasis-"locus" can be found inside Eden, tending the garden and patrolling for strays. And there are strays. Most are desert creatures who drink at the oasis, a few are celestials who knew the path to Eden and sneak in behind its guardians' backs, but it's possible to wander in by accident, too. Like the Library and the Archives, Eden has its quasi-Tethers that even unAware mortals can pass through, and that the Aware can cross inadvertently. None have ever been stabilized -- the only secure Tether to Eden is the oasis, and that's literally part of Eden itself -- but any time enough human belief coalesces around a site, it might create a link. Gardens and groves are the most common Tether-sites, followed by certain archaeological or religious locations: the rumored "true location of Eden" might be entirely made up, but it still might connect to the real Garden, at least for a moment.
Eden isn't all celestial, though; it's corporeal enough that Heaven and Hell can both link to it as the Earthly side of a celestial Tether! Such Tethers are even more frail and unreliable than the corporeal ones, and never end within a Superior's Cathedral, but they're not unheard of. In Heaven, the most common loci end up in the Savannah or the Glade; in Hell, Eden Tethers are rarer than hen's teeth and thus have no established patterns, save for a persistant rumor that Lilith has a private chamber in the Guildhall with a stabilized Tether of her own. (Of course, no one's been willing to pay her price for an answer on the matter.)
As for the Marches, well. People dream enough of the Garden that there should certainly be some tie there, but neither Dreams nor Nightmares has ever reported an ethereal Eden Tether. But you never know what you might find out in the farthest of the Far Marches, out on the very edge of dreaming . . .
[OOC: this is an OPEN POST for anyone, anywhere! Even if your universe doesn't have an Eden, you can wander into this one thanks to the dressing room effect, or into a different one -- maybe a simulation in the Halls of Progress, or an entirely corporeal entity, or just ruins. If your universe doesn't have this particular Eden, you can likewise feel free to cross into this one or play in a different one.
Mechanics for this particular Eden: It's celestial enough that you can wander around in celestial form all you like, and interacting with the world won't create disturbance (whether breaking a tree branch or killing a mortal). Disturbance from other sources, such as Songs, can be heard in Eden and in the oasis, but no farther. It's also corporeal enough that you can wander around in a vessel or living body all you want -- and not only are rolls to perceive celestial forms automatically successful, but corporeal and celestial forms can physically interact. Are you in celestial form and want to pick an apple? A living human who wants to give your batwinged Impudite buddy a hug? Go right ahead! Finally, while it's quasi-celestial, it's not actually a piece of Heaven or of Hell: no Light, no Pax Dei, no spontaneously generated relievers or demonlings, etc. Tethers, as mentioned above, are spontaneous and random: the one you came through might last for years or for seconds, it might be just big enough for you or big enough for an army, and it might come from anywhere and dump you out anywhere. But as usual, if you want or need to tweak anything for your particular scene, feel free!]