Laboratory experiments that focus on protein folding provide excellent opportunities for undergraduate students to learn important topics in the expanding interdisciplinary field of biophysics. Here, we describe the use of Stern-Volmer plots to determine the extent of solvent accessibility of the single tryptophan residue (trp-59) in unfolded and partially unfolded states of the well-studied protein cytochrome "c" (cyt "c"). Comparison of quenching efficiencies for free tryptophan in solution and partially buried in cyt "c" highlights the persistence of residual structure in unfolded proteins and deepens students' understanding of protein structures and dynamics. The experiment builds on our previous laboratory module that probed thermodynamics and structures of cyt "c"; collectively, these protein-folding experiments and related topics provide physical chemistry students with opportunities to explore a comprehensive set of spectroscopy and biophysics tools. (Contains 3 figures and 1 table.)