One of the most fun ways of learning is through games and quizzes
. If you do a quick Google search, you can find quizzes
on just about any topic, including math, grammar, the U.S. Constitution ... you name it. Also try flashcards for effective learning.
Art a day. If you'd like to learn about art, one of the best tools is Your Daily Art. Subscribe to the feed, and every day you'll get a famous piece of art, along with some notes to help your contemplation.