Downtown's cast-iron district is the best architecture walk in the city, and almost nobody walks it for the buildings — they come for the shops and miss the columns holding the shops up.
Start on Greene Street, the densest stretch of cast iron anywhere: whole facades of moulded columns and cornices, iron painted to pass for stone, cobbles underfoot. Walk the middle of the street and keep your eyes up. Drift across the retail core around Prince and Mercer, where the chain stores fill the ground floors of the same iron-front buildings, then cross Canal — and the crowds simply stop.
South of Canal is Tribeca, the warehouses gone residential, the streets laid in Belgian block, far fewer people. This is a walk to take aimlessly; let the quiet blocks pull you along. Find Duane Park, the green triangle left from the old butter-and-egg market, and sit a while. End on the Franklin and Chambers blocks the film festival borrows each spring, with the 1/2/3 a couple of minutes on.
