Ultimate Riddle is a "levels" game.
You will have to solve a riddle to find the word that will grant you the access to the next level.
Every level contains useful hints (in the source code, in the picture, in the page itself etc.) to find the answer.
You'll have to search everywhere.
The answer to go to the next level must be (almost) ever entered in the following way:
If the level's URL is
http://ultimateriddle.altervista.org/dolphin.htm
and the riddle answer is "pop", then you have to write
http://ultimateriddle.altervista.org/pop.htm
In some levels you will find a Google Searchbar. Sometimes, to solve levels, you will need to perform a search.
If there's no Google searchbar, a web search isn't useful to solve the riddle.
Wikipedia is also recommended.
You can take a look at forums for extra hints.
Add each level in your bookmarks. They could be useful!
