Except for its saucy rows of opaque lemon awnings, the four-story building next to the Düsseldorf railway station might almost pass for a clinic. Attendants carry stacks of fresh linen through its quiet halls. Its pleasant central dining room keeps hospital hours: breakfast from 8 to 10, lunch at noon, dinner at 5. Its 228 tenants, each of whom is examined by city doctors at least twice a week, spend most of their time in bed.
But not alone. The $875,000 establishment, built three years ago by an enterprising female real estate speculator, is the biggest, shiniest and...