Most people don’t go to Longwood Gardens for the cream of mushroom soup, pan-fried crabcakes with rémoulade sauce and a glass of Chaddsford wine, but maybe they should. The Terrace Restaurant at Longwood Gardens is an exceedingly understated dining room in the midst of this American Versailles created by Pierre S. du Pont. Indoor greenery is minimal, and during a lunch visit, the dining room was nearly as hushed as a library. Reservations are advised for lunch, served daily, or dinner.