If you want to leave a place, you need a means of egress, or a way to exit, such as a door or window. It was a beautiful old house, but without enough ways of egress, they needed outdoor fire-stairs for reaching the upper floors.
Egress comes from a Latin word meaning "going out." An egress is basically the same thing as an exit. (Egress can also be used as a verb, "to exit," but less frequently than as a noun.) When buildings undergo inspection, one of the main safety features under review is the number and placement of doors and windows, the "means of egress," in case of fire or other emergency.