Yep, I remember that level. My sister and I called it the Pepsi Maze, because of its maze-like layout and the fact there were Pepsis everywhere.

I believe this is the secret level: https://www.commander-keen.com/level-maps-1.php

We called it the Teddy Bear Maze, for its higher occurrence of teddy bears than other levels. Though looking at the layout now, I don't think it quite deserves the 'maze' designation as much as the Pepsi Maze does. But all those teddy bears...you could rack up a few extra lives if you managed to snag them all.

Looking at the levels, this one raises my curiosity: https://www.commander-keen.com/levelmaps/1/015.gif Note that there is a yellow keycard, but not a yellow door. I'm thinking either the level was never quite completed, or whoever took the screenshots to make these images took one after opening the yellow door. Reflecting on it now, I think perhaps the latter was the case, though I don't remember where the yellow door was. Either by one of the robots, or right before the drop out of the colored area.