Abstract: A mountaineering boot having: a vamp designed to accommodate the user's foot and ankle, roughly up to calf height; a sole unmovably fixed to the bottom of the vamp to cover the underside of the user's foot; a substantially sock-shaped outer gaiter which completely covers the vamp grazing the outer surface of the vamp up to the top of the bootleg of the vamp; and a zipper which extends along the gaiter to allow the user to open the gaiter for access to the vamp underneath, following a substantially spiral-shaped, curved path which begins behind the front portion of the gaiter, and ends at the upper mouth of the bootleg of the gaiter, after following, in the end stretch, a substantially helical trajectory about the axis of the bootleg that crosses the rear part of the bootleg of the gaiter.