In Quake's single-player mode, players explore levels, facing monsters and finding secret areas before reaching an exit. Switches or keys open doors, and reaching the exit takes the player to the next level. Before accessing an episode, there is a set of three pathways with easy, medium, and hard skill levels. The fourth skill level, "Nightmare", was described by the game manual to be "so bad that the entry is hidden, so people won't wander in by accident".[16]