If one is afflicted with melancholy, he should cure it by listening to songs and various kinds of melodies, by walking in gardens and fine buildings, by sitting before beautiful forms, and by things like this which delight the soul and make the disturbance of melancholy disappear from it. In all this he should aim at making his body healthy, the goal of his body’s health being that he attain knowledge.

Rambam, introduction to commentary on Mishna Avot, "Eight Chapters on Ethics", chap. 5.  298