First go to primer.php and guidance.php as per the riddle title.

In the center of the image in guidance.php is an “Unholy Bible”, and the image text reads “LaVey”. Googling reveals that the book in the middle refers to the Satanic Bible, which is comprised of four books:

The Book of Satan
The Book of Lucifer
The Book of Belial
The Book of Leviathan

If you look up Lucifer on Wikipedia you will find that it means Morning Star. Belial has been called the worthless, and DCLXVI is roman numerals for 666, which is loosely the number of Satan. Hence the last book, with the question mark, must be The Book of Leviathan.

Clicking The Book of Leviathan takes you to furtherguidance.php.

Read about the Book of Leviathan to learn that it contains Enochian Keys, symbolized by the keys in the image. The meaning of the direction of the arrow has thus been established. Since there is another arrow pointing away from the keys, namely to the red pentagram, this must mean that whatever the red pentagram symbolizes, must also contain the Enochian Keys. Hovering the pentagram, gives the word “Magic”. A magic that happens to contain the Enochian Keys is Enochian Magic.

The pentagram has two arrows pointing toward it, which, based on our established meaning of arrows, means that Enochian Magic contains (or consists of) six books. Reading about Enochian Magic confirms that indeed it does, and that the sixth book, which is hilighted in the image, is called Liber Loagaeth.

Go to liberloagaeth.php (or liberlogaeth.php seems to work as well) to find a digital copy of this book. You will find it is full of “Leaves” which is basically a bunch of grids of symbols.

Go back to the main page, towerhalls.php, and you will quickly realize that 17A, 20B, etc refer to different grids in the book. You are given a bunch of coordinates in the different grids, [R,C] meaning that the first number indicates row and the second number indicates column.

From here it is pretty straight forward. Find all the symbols the coordinates describe and then use the primer.php to translate those symbols into letters. Note that RGLUCEDG has two G’s in it, the second letter and the last (8th) letter. Similarily, one of the strings of symbols has the same symbol in place 2 and 8 which suggests that string of symbols is simply RGLUCEDG written in symbolic.