Behold! A small chain of riddles has been placed on the Derelict World album. Solving this quest you might find the entrance to the promised land of the bonus world and you will become an esteemed hero on the Wall of Fame.
All you need is the CD version of the album (including the booklet) - I'm sorry, but MP3 versions from iTunes/Amazon/etc will not work at all - and your brain. As a final step you will need to enter your name which is then carved into the Wall of Fame.
Be aware that the quest is only solvable by true heroes. It is rather difficult, but there are at least three different paths you can choose from.