Over the next couple of years I am going to study geometry more thoroughly. I have been reading a lot of quick-study guides such as Geometry Demystified. These books are too simple and don't get deeply into issues. Finally I just ordered Euclid's 13 books of The Elements.
On p. 1 of the introduction it tells an anecdote in which Euclid was asked by Ptolemy the king of Egypt for a brief course that would allow him to understand geometry more quickly than the hoi polloi. Euclid replied that there is no "royal road to geometry."