A fluid-structure interaction (FSI) experiment was designed and executed to produce low-frequency (~10 Hz), high-amplitude (±3.5% of the span) motion of a fin. This was achieved by placing an Inconel swept-fin at -9.6° angle-of-attack within the wake of a roughened cylinder. Speeds between 2.5 and 3.6 m/s produced cylinder diameter-based Reynolds numbers between 190,000 and 280,000, respectively. Detailed descriptions of the geometry, material/structural behavior, fluid properties, and initial conditions are provided to facilitate computational model development. Given the initial conditions, the resulting forced fin behavior was characterized with measurements of the mean and fluctuating velocity upstream of the fin (i.e. within the cylinder wake), fin-tip/surface motion, and the fin constraint forces/moments. This work provides a detailed experimental dataset of conditions mimicking a crashback event that is also a challenging FSI benchmark problem involving turbulent, vortex-induced motion of a structure. It has been used as a validation condition for FSI simulations, and the data can be used to validate other FSI models as well as identifying strengths and weaknesses of various FSI modeling approaches.