ToME WikiDim Gates is a SpecialLevel on Dungeon Level 85 of the dungeon Angband. You'll find the Ring of Power 'Narya' in this level.
The level's full name is Dimensional Gates, and as you might expect, there are void jumpgates aplenty. There are also lots and lots of inconveniently situated Quylthulgs (various breeds) and some random monsters. The Quylthulgs make the level tricky and you need to be able to handle getting into line-of-sight of several of them while they all are several squares away from you. The void jumpgates make the level confusing, but actually work to your advantage, as you can use them to teleport out of reach of your enemies and heal.
This special level continues a trend that many other special levels have set of being really mean to straight-up warriors, who tend to have sub-par ranged attacks (pointless once they're surrounded by summoned monsters anyway) and no way to muck with line of sight. Pretty much any LOS-disruption will be incredibly helpful when it comes to dealing with Quylthulgs, since they don't move on their own. You'll still have to suffer at least one round of their ministrations though before you can get the spell off, because many of them are in sight of the gate that you just used.
Ring of Power 'Narya' can be found at the end of a long, curving, several-squares-wide, optional corridor that is filled with deep lava and populated by Greater Hell Wyrms. Having fire immunity already from another source before trying to get Narya is greatly recommended. The Ring of Flare makes this a cinch, since you can just skip the entire level by switching places with one of the wyrms, nab the ring, and get out. Flare is cheesy.
Chatter
MayLith: Anyone have more info than this? Please?
NerdanelVampire: Glad to be of service. I added some more info.