Originally Posted by Myrgrim
I'll go ahead and roll for all relevant knowledge categories regarding Hellgate Keep.
- This one is a bit far-fetched I'll admit, but you never know.
Hellgate Keep's magical aura was muddled, to say the least; several different variations of magic were implemented in the location over the centuries. The site's title; Hellgate, is only truly reflective of its inhabitants two tenants past, since then the infernal was mingled with demonic, then after its destruction a natural magic has taken root there.
The site for Hellgate Keep was once, many years past, elven by make. The framework for all later structures were erected on this infrastructure. While the site is currently primarily a crater; it is suggested that elven, infernal, and demonic ruins; as well as structures used by those who fought the extra-planar inhabitants may very well be buried below the destruction. Evidence to support this idea is solidified by the knowledge that the demonic inhabitants constructed tunnels to circumvent measures implemented to restrict their portal abilities. These tunnels were known to stretch as far as the Neither Mountains before the Keep's destruction.
Specifically towards the planes check, that information is covered in the above two results.