Here are the level codes for all the levels, even the bonus levels. These codes will let you start the game at different locations without having any of the levels completed. These codes may not work on all versions, as there are different versions of the game.
"BHEAEALK"-----Lava Castle | "BHEAHAIK"--Checker Castle
"BHEAGAJK"--------The Cave | "BHEABAOK"----Fishy Castle
"BHEAAAPK"-------The Mines | "BHEADAMK"------Cog Castle
"BHEACANK"-----The Outside | "BHEANACK"-------The Cloud
"BHEAMADK"-Stepping Stones | "BHEAPAAK"--Conveyer Belts
"BHEAOABK"-------The Boats | "BHEAJAGK"--------The Cave
"BHEAIAHK"-------The Boats | "BHEALAEK"-----The Outside
"BHEAKAFK"-Stepping Stones | "BHEAFBKL"-The Lost Castle
"BHEAEBLL"-----Bonus Round | "BHEAHBIL"-----Bonus Round
"BHEAGBJL"-----Bonus Round
"AHEAFALK"-First Code | "OIEAFAFF"-Second Code | "OIHAFAIK"-Third Code
STEAM CASTLE--"AHJBEAEA" | CHECKER CASTLE--"MPDNGAMF"
FISHY CASTLE--"MODNAAOG" | COG CASTLE------"MKDNCAIK"
LAVA CASTLE---"OKDNFAPK" | CONVEYOR BELTS--"OIHMOACO"