Thundenstone, a holy place of the gnomes (a cavern strong with natural radiations, used by gnomes to charge magic items in a manner very similar to the Earth Nodes detailed in the 3e Underdark sourcebook), where about forty gnomes dwelt, keeping very quiet so as not to be noticed by other Underdark denizens. This policy had failed, and after several bloody battles against drow, the gnomes provide shelter to all non-drow in return for aid in battle, payments, needed goods, and promises of future aid.
Thundenstone was “deep in the Underdark,” where Halaster’s wards start to fade, and gnomes who know how can ‘tap the node’ (exhausting it for a day or so) to use it as a one-way portal (outbound).
This is an excerpt from a larger article available on Ed”s Patreon, which Ed narrates himself!