The effect of coming accidentally upon the Washington Mews, a small cobblestone alley of stable houses, some renovated and some preserved, that once served the wealthy homes of Washington Square North, is of strolling suddenly into a secret urban garden. If a single block set in a bustling city can seem idyllic, it's this one; the air is always crisper, the sun a bit brighter here. Though, like most of the buildings that line Washington Square, most of the carriage houses here are now owned and operated by neighborhood omnivore NYU, but they retain a real nineteenth century charm.