Waterfall is Undertale's third area and middle point, following Snowdin and the Papyrus boss fight. The following is designed to be played as part of a complete Pacifist guide - in short ...

Papyrus is the second major battle of Undertale, following the completion ... leave town to the east to Waterfall, the game's third area and another filled with enemies to spare as you continue ...

(on PC you use arrow keys, not WASD to move). In Undertale you will make your way through different as you try to escape the Underground. The first area you'll encounter is the Ruins.