At TheRivendell Bar & Grille (920 Studemont, 713-564-3700), there is a magnificent mural of that mystical land of the same name from J.R.R. Tolkien's TheLord of the Rings. There is also a dish called shrimp gambary ($10), which may well have mystical powers. All it took was one bite to transport me to another world. A puff-pastry shell, known as a vol-au-vent, is filled to overflowing with lump crabmeat. Scallops and shrimp swimming in a sea of sauce seem to cascade from all sides. And the cream sauce, touched with tarragon, is ethereal. This is the kind of food from which fellowships are made.