Only just discovered this game which is really nice. Upon loading it asks for a TAB file to load the designer level (just type in "HAL".
Unsure why the Level Editor for this game has been Hidden, the designed level has a nice difficulty to it, although I found the 1st screen rather tough, though it kinda needs to do that to set you up because not everything is what it seems with Hidden Squares and even the odd regular Brickwork having a Gem behind it!