Fantasy is a rather complex genre. However, the concept of fantasy is simple. This causes fantasy to be broken down into many different sub-genres to specify. The main sub-genres of fantasy are: epic, heroic, contemporary, and urban. Epic fantasy, also known as high fantasy, is massive in scope with a large cast, high word-count, and an intricate plot. J.R.R. Tolkien and Robert Jordan were prolific epic fantasy authors. Heroic fantasy is less complicated and generally shorter than its epic cousin, with action and danger very prominent. Contemporary fantasy is the simplest fantasy sub-genre in theory, although it can be broken down into further categories that can be experimental, fresh, and more literary. Urban fantasy stories take place in urban settings, often with a secondary world or plane coming into contact with our world. Harry Potter and Percy Jackson and the Olympians are series that can be put under both urban and contemporary genres, while another of Rick Riordan's works, the Kane Chronicles, is moreso the later.