No, this isn't the Arch of Ages; this is the inspiration for it.
The Arch of Ages is a powerful artifact that is located in a huge, underground cavern deep within the Mounds of Dawn, in the Perrenlands. It is an archway which measures 20 feet wide from outer edge to outer edge, and the top outer edge of the arch is exactly 30 feet high. The inner arch dimensions (the "empty space") make it 14 feet wide at the base, and 27 feet high at the top center apex. The arch itself is a 3-foot wide band of stone, which is covered in epic-level magical runes.
The archway is indestructible by any means short of divine intervention (including Mordenkainen's Disjunction) and is invisible to the naked eye. It is affected by a powerful dweomer which causes the archway to remain ethereal, until someone affected by True Seeing approaches with 20 feet of it. When this happens, the archway materializes onto the Prime Material Plane, although it remains invisible.
The ground (both above, and below) within a half-mile diameter around the archway is also affected by a dweomer which makes it incredibly hard to dig. That is why nothing has ever been built near it or around it. Those who have tried have become frustrated and given up, some even saying that the land is cursed. Only the most perceptive and intelligent people realize that there is magic present here, and that the area was meant not to be disturbed.
Since it is an artifact, Detect Magic will not reveal the presence of either the archway, nor of its associated dweomers. The archway was made by the goddess Wee Jas, and it is well-hidden for a reason.
Anyone who can see the archway will notice that the runes inscribed upon it are always in motion, slowly flowing back and forth, like the waves of a restless ocean. In order to make use of the archway, a person (creature) must be an epic-level spellcaster. In addition, he or she must possess sufficient spellcraft skill levels, as described below. Non-epic spellcasters with sufficient spellcraft skills can understand the archway's functionality, but they cannot make use of it.
Spellcraft Base Skill 14 and below: The caster can discern that that the archway is for magical travel, but nothing specific.
Spellcraft Base Skill 15-19: The caster can use the archway to teleport himself or herself, and others as well, to any location on the Prime Material Plane (Oerth), as if using the Teleport Without Error spell.
Spellcraft Base Skill 20-24: The caster can use the archway to teleport himself or herself, and others as well, to any location on any Alternate or Parallel Prime Material Plane (i.e. worlds other than Oerth), as if using the Teleport Without Error spell. Note that the Teleport Without Error spell does not normally allow inter-planar travel. The archway's abilities, however, are epic in nature, allowing it to overcome this limitation, as long as the caster has sufficient skill to do so.
Spellcraft Base Skill 25-29: The caster can use the archway to shift himself or herself, and others as well, to either the Ethereal Plane or to the Astral Plane, as if using the Plane Shift spell.
Spellcraft Base Skill 30-39: The caster can use the archway to shift himself or herself, and others as well, to any of the Inner Planes, as if using the Plane Shift spell.
Spellcraft Base Skill 40-50: The caster can use the archway to shift himself or herself, and others as well, to any of the Outer Planes, as if using the Plane Shift spell.
Spellcraft Base Skill 51+: The caster can use the archway to shift himself or herself, and others as well, to the city of Sigil, as if traveling by portal. NOTE: A base skill of 51 in Spellcraft requires a total character level of 48!
Please note that until one's base spellcraft is extremely high, making use of the archway is a one-way trip. Once you get where you're going, you'd better have a good way to get back.
Spellcraft Base Skill 61+: The caster can use the archway in any manner listed above, with the additional effect of a "temporary" gateway being opened at the destination point, through which any number of other beings can pass from the destination point onto The Prime Material Plane. The gateway is the same size as the dimensions of the inner arch (see above) and has an indefinite duration. The gateway has the same properties as the Arch itself, except that it is completely visible to all. Anyone with enough skill can command it to collapse. Collapsing the gateway must be done from the destination point, and requires an epic-level spellcaster with a base spellcraft skill of at least 50. Once the portal is collapsed, the spellcaster must then have an alternate means of returning from whence he or she came. It is for this last power that the secret of the archway is so heavily guarded. More than one demigod and/or demon lord has tried to use the archway for the conquest of the Prime Material Plane. Fortunately, none have ever succeeded. It is also rumored that this last use of the Arch's power can affect one's passage through time, i.e., that one can not only travel to where he or she desires, but also to when he or she desires, whether past, present, or future. This last aspect has never been studied by anyone in great detail; those that have attempted to study this aspect have all disappeared quite suddenly, never to be heard from again. NOTE: A base skill of 61 in Spellcraft requires a total character level of 58!
The Arch of Ages was meant for use by mortal agents of the gods, so that they may quickly be transported to wherever their patron deities need them to go. All of the gods of the Oerth Pantheon approved the creation of the archway, but it was Wee Jas who actually created it.
Mortal agents who are on errands for their respective deities (i.e., The Chosen) often carry special spell focuses, which allow them to use the Arch as if their base skill was 51. These focuses usually take the form of amulets, rings, or specially enchanted weapons. The focuses work only for the person that the deity keyed them for. And they work for that person only so long as they remain within the deity's favor. A deity must be of Intermediate Rank (Divine Rank 11+) in order to make such a focus for a follower.
As an example, Hawke and Nimbar both carry such focuses, and use them not only to work the Arch, but to cast epic level spells as well. (See: Major Trinket, and Minor Trinket description on most of their epic spells.) Both trinkets were crafted and blessed by Nimbar in the name of Odin. Afterwards, Odin keyed the Major Trinket for use by Nimbar, and Thor keyed the Minor Trinket for use by Hawke. Of course, Nimbar is powerful enough nowadays to use the Arch without the aid of a focus, and Hawke knows enough to reach the Inner Planes without resorting to the use of his focus.
NOTES: Using UMD (Use Magical Device) Instead of Spellcraft:
DC to Emulate an Epic Spellcaster (Using Total Skill Rating): 42.
Other DC Adjustments:
( BASE RATING:........................Description )
34 and Below:............................It's for magical travel.
35-39:............................................Teleport w/o Error
40-44:............................................Alternate Prime
45-49:............................................Ethereal or Astral
50-59:............................................Inner Planes
60-70:............................................Outer Planes
71+:................................................Sigil
81+:................................................Temporary Gateway