Kitchen: Really a superflous room, Vader mostly used it to choke people

Rooftop Patio: On rough days, Vader would go up here, look down at an effigy of Obi-wan below, and shout "Now I have the high ground!"

Zen Garden: To really get the dark side going in him, Vader would come meditate here and look at the sand. The anger would flow through him at this point.

Kitchen: Vader always kept a fully stocked kitchen and a full staff on duty at all times despite not actually requiring food himself. Vader himself lived off of a diet of the Force and nutrients that his suit simply pulled from the air. Once a week it was one staff members duty to throw out all food in the kitchen and replace it all. Among the staff of Vader’s castle, kitchen duty was the most sought after due to the fact that no work was required.

Bedroom: Vader’s palatial bedroom puts the bedrooms of many royal families to shame, with its massive round bed that raises and lowers from the floor, the picturesque views of the Mustafarian landscape and the enormous walk in closet that is larger than the bedroom itself. All of this was in fact for the ladies. Vader liked to show off for the ladies and though he himself never slept but instead just meditated for a few hours a day, he still maintained his playboy persona with his castle, and in particular this bedroom.

Indoor pool: Surprisingly Vader kept someone on staff 24/7 with the sole duty of maintains the pool. Only one person was ever allowed to swim in the pool, Emperor Palpatine, who absolutely detested the heat. It was actually one of his conditions when allowing Vader to construct the castle, he needed to have a place to cool down when visiting Vader’s vacation home.

The Master Bath: The plumbing for Darth Vader's personal toilet actually utilized lava in order to help him overcome the personal trauma the substance had dealt to him in the past.

Vader's Closet: Apparently, a stormtrooper once stumbled upon a droid that was wearing a wig and Padme's clothes in this closet while cleaning Darth Vader's room.

Vader's Trophy Room: These ten pedestals once held the skulls of Jedi Younglings that Vader killed when he raided the Jedi Temple.

Small platform on the edge of the cliff right below the main hall: Vader used to come here to sit and watch the lava flow. Sometimes he would use the Force to manipulate the lava in strange shapes along the other cliffs.

Northwest sphire: Place where most people, if any would stay for the night.

Landing platform: It’s rumered that there is a piece of Anakin’s old fighter embedded in the platform itself.