Quest to the Native or QTTN is a type of Foldit puzzle which features a translucent gray guide showing the native shape of the protein. The goal of a QTTN puzzle is to fold the protein to match the guide as closely as possible.
QTTN puzzles have been largely replaced by electron density puzzles, but there's still a Quest to the Native puzzle in the Foldit intro puzzles, and also a beginner puzzle called Parabacteroides Distasonis which features a guide.
With the "show stubs" sidechain view option selected in View Options, hovering over a sidechain stub on the protein extends that sidechain and the corresponding sidechain on the guide, allowing easy identification of the corresponding segments. Bands can be created from the protein to the guide, helping to reshape the protein during a wiggle, rebuild, or remix.