Eye tracking research in art viewership is often conducted in a laboratory setting where reproductions must be used in place of original art works and the viewing environment is less natural than in a museum. Recent technological developments have made museum studies possible but head-mounted eye tracking gear and interruptions by researchers still influence the experience of the viewer. In order to find a more ecologically valid way of recording eye movements while viewing artworks, we employed a prototype of a calibration-free remote eye tracker hidden below selected paintings at the Kunsthistorisches Museum in Vienna. Museum visitors were unaware of the study and informed post hoc that we had registered their viewing behavior and asked to give consent for the use of their data. This article presents the study design as well as results from over 800 participants. While the data quality from the eye tracker prototype was not sufficient to conduct the intended analysis on within-painting gaze movements, this study might serve as a step towards an unobtrusive examination of the art viewing experience. It was possible to analyze time spent viewing paintings and those results show that certain paintings consistently drew significantly more prolonged attention from viewers.