Perched atop majestic London Terrace, a Depression-era development in Manhattan’s Chelsea neighborhood, this 2,600-square-foot residence started out as a dark and claustrophobic four-bedroom apartment, emerging after a massive renovation as a spacious and light-filled one-bedroom penthouse. A simplified and largely open plan organizes the home on two axes, allowing views through its rooms and to skyline vistas beyond. A series of 22 new glass-and-steel French doors and windows replaces original small window openings, maximizing these views and allowing access to a wraparound terrace. Newly created spaces include a master suite with a bedroom and two bathrooms; an enfilade of rooms connecting the living room, library and study; and an eat-in kitchen designed for easy entertaining. The interiors feature the clients’ collection of antiques and art, as well as new and custom-created pieces and luxurious textiles.