Nobles are cursed with highly refined tastes that are difficult to satisfy. Coincidentally, they often fall prey to tragic accidents. Here are some tips to keep your nobles safe.
What could be more dwarven than a menacing spike? Better make it retractable, in case your noble needs the space. Put this steely symbol of dwarven strength in one of your noble's rooms, possibly next to the lever. Nobles LOVE Masterwork Menacing Steel Spikes encrusted with precious gems, and it boosts their room value. (Maybe.)
Any dwarf of such high standing should also have a lever in his rooms. If he should find himself stressed by overdue mandates, or accidentally locked in his room, he can amuse himself by pulling it repeatedly. Pulling levers is one of the few tasks only fit for nobles, after all. A lever can be made personal to a specific noble in the p | q Profile for that lever, just as if it were a common, lowly workshop.
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All dwarves love the soothing mist of a waterfall. Why not give your noble one, right in his very own room? Take care that the drainage system is working properly. Any obstruction could cause the room to fill with water, and no one wants that. Remember to put an attractive grate over the drain, to keep anything from falling in and stinking up your plumbing.
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Your highest noble will meet with various visitors and emissaries in his throne room. To give him that extra edge in negotiations, make it intimidating. Put a magma pool right there in the throne room. No glittery gold throne, either. Make one out of iron, or steel, or some other material with a high melting point.