For the code:
look closer at the coin!
Move your cursor till a number appears (near the symbol that looks like a door)

I don't know what to do with that ancient coin. I don't see numbers and I'm stuck. There are no clues as to what I'm supposed to be looking for. I stared at that coin for 5 minutes and I see nothing that can help me.

An old favorite of mine is this series of games. I recently rediscovered Newgrounds again and decided to play some oldies. Not quite as polished as the later entries, and a bit cryptic at times, but definitely over all well done.

Can someone tell me a brief explanation of how to use the Ancient Crystal of Wisdom?

Not bad, needs a map, but that would not be fun!