In English, a "castle" is (typically) a building built for protection or fortification. It can, but doesn't have to be, pretty fancy, but its primary function is defense. A "palace," on the other hand, is (typically) a building built to show off wealth, power, and/or importance, but it's not necessarily the best place to be during a battle.

Having said that, in day-to-day 21st-Century English, the distinction isn't always so clear.

For Klingons, the distinction is also a little murky, since they would never construct a "palace" (a home for the emperor or some other important person) that was not designed deal with battles. They might construct a "castle," though, that wasn't particularly lavish and not a suitable place for an official residence of the emperor.

The word for such a structure - elegant or otherwise - is jem'IH. The emperor's castle/palace is simply ta' jem'IH.

If, however, the emphasis is to be on the elegance or grandeur of the jem'IH, there's another word that can be used: DuHmor. A DuHmor is a type of jem'IH, so it's a good place for the emperor to hang out. For clarify, you can say ta' DuHmor. The emperor's official residence would more likely be referred to as a DuHmor than a jem'IH, but not necessarily always.

Klingon ships, of course, are battle-ready, so any ship designed to be the residence of the emperor might, I suppose, be referred to as a jem'IH or ta' jem'IH. And if it's a particularly grand place, then DuHmor or ta' DuHmor could make sense. (Maybe those are short for jem'IH Duj and DuHmor Duj.)

http://lists.kli.org/pipermail/tlhingan-hol-kli.org/2018-January/006925.html