An air seal unit to be positioned adjacent blade structure in a gas turbine is provided. The air seal unit comprises a main body including a plurality of first impingement cavities and at least one first interconnecting passage extending between and communicating with a first pair of the first impingement cavities. The first interconnecting passage is nonparallel to the first pair of the first impingement cavities and defines a path for cooling air to pass from one impingement cavity of the first pair of the first impingement cavities to another impingement cavity of the first pair of the first impingement cavities so as to strike a wall defining at least a part of the other impingement cavity of the first pair of the first impingement cavities.