Thomas Sandby (1721/3–98), who served as the Royal Academy's first professor of architecture from 1768 to 1798, shaped his students’ architectural thought. His lectures represent some of the crucial developments in viewing architecture that occurred during the period. They are vibrant expressions of how a viewer's experience of buildings informs architectural teaching and design, and demonstrate the importance of architectural experience for eighteenth-century architectural thought. This article explores Sandby's thinking, first in his own observations of buildings in his diary of a tour through Yorkshire and Derbyshire, and then in his teachings, which functioned as a kind of manual for future architects. It examines the diary and the lectures for his ideas on the effects of architecture — a building's situation, exterior, interior and decorations — in relation to the picturesque, one of the dominant concepts in his texts and drawings. Sandby's architectural thought is shown to be a relatively early statement of the picturesque applied to architecture and its setting.