Invest in Yourself
One of the best investments you can make at any time of your life is in yourself. This doesn’t change after retirement; in fact, many doctors suggest that retirees continually challenge themselves mentally to stave off the deterioration that sometimes accompanies old age. Invest in a good online course in a topic that interests you, or better yet, invest in an on-site course that requires you to interact socially with other students of all ages.