The Eye of the Beholder is required for the potion. The heroes must descend to Bottom World's very core.
Did You Know?
In the Cave of Sloth, Brogan Josh states that if it takes 1 man 2 minutes to check 1 key, it will take 237 years for 4 men to check 1 billion keys. That answer is out by a factor of 4; it will actually take just under 951 years.
The answer given by Dick, 7 litres, is also incorrect. See more
Normally we just go into the forest, find a weirdo, and get the ingredient off them.