The desire to give Darth Vader his own personal abode dates back to production of The Empire Strikes Back. Famous concept artist Ralph McQuarrie actually created a piece for Vader's castle at the time, with original artwork that consisted of rounded towers and a snow-covered landscape. George Lucas wanted
to use fire and lava instead, to evoke hellish imagery more synonymous with evil. Lucas' concept was even modeled for Episode V, but didn't make the cut. Vader did eventually get his own castle, but only in the non-canon stories of the expanded universe.
This piece was actually created in early stages of The Force Awakens, where McQuarrie's snowy fortress and Lucas' evil hellscape were fused together to create a sinister design akin to Dracula's castle. It was eventually reworked and used in Rogue One: A Star Wars Story, with a much less interesting look. Rogue One's blackened and streamlined castle on Mustafar works just fine, but the majesty of this unused concept is hard to pass on. Between the beautiful contrast of the snow and fire and the sheer scale of the fortress — how didn't this epic design get the nod?