Hints could be in the text, the source code, the pictures, everywhere!
Sometimes you will need google or Wikipedia.
Sometimes you have to search in different languages.

And sometimes you have to use your brain.

When you think you have the right answer, just change the word before ".htm". E.g.: If the answer is "side2", just change:

/riddler_on_the_roof/side1.htm

to

/riddler_on_the_roof/side2.htm

If the answer has more than one word just type the words without a space: e.g.thankyou instead of thank you.
Type the answer in lowcase letters!

Right click anywhere on the web page (except pictures) whose source code you wish to view.
In the context menu, click on "View source".

Cheating is possible. But it only proofs that you are too stupid, to solve the riddle on a legal way.
If you are stuck, visit my forum: Forum
To post there you first have to register - sorry, I know, it sucks, but there is no other way.

The riddle is very easy - but I hope you enjoy it!

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