Yesterday, it was Oliver Wendell Holmes Jr.'s old haunt on Chestnut Street built in 1824. Today it's a townhouse just doors down and built 15 years earlier. The 4,176-square-footer has 4 bedrooms and 4 bathrooms (two halves), and a formal dining room with 14-foot ceilings and the original marble mantel. There is the thoroughly modern touch of central air as well and an elevator between the four floors. The townhouse last traded in October 1995 for $1,350,000, and is now asking $4,250,000.