Caves of ZZT
From classicdosgames.com description:
"ZZT is an ASCII adventure along the lines of the famous Kroz series. The hero can move from screen to screen, fighting monsters and collecting treasures as he goes. ... ZZT is known for clever level design and use of the 16 color palette, and also uses the PC speaker to create music more effectively than most games of this era. The game also came with a level editor, inspiring thousands of user-created levels. There is still a fan following for this game even today. Epic released the full version of this game as freeware on their website in 1997."
Caves of ZZT is the second volume of the ZZT series.