Somehow you’ve gotten your dream home. The cabin in the mountains, penthouse downtown, castle nestled deep in the woods, nuclear bunker in the hills, or whatever. Whats the bit you’d add that might raise a brow from others? The fireman’s pole? The slide? The moat? The hidden room behind a bookshelf where you keep your stuffed animals?
A music room, with space for my decks and records, top notch sound system, perfect soundproofing on the walls, a lighting system, a small dancefloor, a bar. Also, it would be hidden behind a bookshelf, as described in OP.