As everyone knows, the world is flat. Avalon is the central and most massive continent, bordered on the north by vast and impenetrable mountains and to the west, south and east by the wine-dark sea. Beneath the surface of the Avalon continent, be it mountain or hill, or river or farmland, are hundreds upon hundreds of feet of "under-deeps". These under-deeps are accessible only by happening upon fortunate entrance points: like tunnelheads, or trenches that have been extended. Delving into the under-deeps, creating networks of tunnels and exploring beneath the continent, is a major facet of warfare in the land. See HELP TERRAIN should you have an interest there, and HELP LOCALE or HELP LOCALEPOINT for information on the interplay of your current location atop the "under-deeps".
But what are these "under-deeps", besides convenient covert tunnel potential for legions? Beneath Avalon are many, many other features besides the standard stone-and-soil through which tunnels are dug: caves, some hidden for millennia, riddle the under-deeps. Within these mysterious caves, many are merely empty, or have but an underground river a-flowing through... but some contain treasure, artifacts; the occasional cave may have been the hidden refuge of forces of greater, more frightening import: monsters from the Divine War, creatures of the id. Waters flow through the land at many layers, underground lakes are not uncommon and flood-waters occasionally burst forth - sometimes by design - wreaking havoc through the tunnels and, now and then, spilling over onto the surface. The Avalon continent has a smattering of volcanoes, too, fed by magma trails trapped within the under-deeps. Encountering these - potentially releasing explosions of lava, can have catastrophic effect.
Down further we go, hundreds upon hundreds of yards below the blithe and familiar surface world. Passing the stone and the soil and the caves and the waters and the magma and whatever-else makes up the under-deeps: eventually to a seam of granite, fused by the Gods themselves. Below the granite 'ceiling' lies the nether-world, domain of the ethereals, the poltergeists and touched by the thaumaturgist: therein are sunk the roots binding the seeing stones to Avalon, and the Seer profession dabbles in gateways twixt the two realms: the top and the bottom of the world. What lies beneath the nether-world? There is nothing but the Void. Beside the nether-world sits the under-world, described in HELP UNDERWORLD. And that is all we know...
