They cheerfully greet you, “Welcome aboard!” And then the trip begins. You can enjoy breakfast, lunch, and a pre-dinner aperitif on the Tiber River. At sundown, Baja transforms from something resembling a wood-and-glass ship (it was a barge in its previous life) to a club cum lounge. The bartenders serve cocktails and specially selected wine, while “the captain,” Luciano Costanzo, cooks up contemporary interpretations of Italian classics, like spaghetti and clams or tuna steak.