How do I get to the hidden levels?
By looking at the source, I've found a couple of 'hidden' levels, but not how to get to them. They are as follows:
desert
seas
Cow level
How do I get to them?
The desert can be reached by using a Get me Out of Here (G.M.O.O.H.) potion. The things you can possible end up in by using a G.M.O.O.H.-potion are:
The peaceful forest
CowLevel
sea
desert
They have an equal chance of happening.