Secret City
The Secret City is a secret level in Keen 1. It is hidden in the dark side of Mars, behind a chain of mountains. This level can be reached by using the hidden teleporter in Red Maze City. It is one of the few levels in the game with an official name, given in the printed game sheet.
This is one of the biggest levels in the game. It is made out of red bricks mostly, and has several winding passages. There are no robots in this level, only Yorps and Gargs. Though it is relatively easy to get to the exit, the idea of the level seems to be to explore it to get as many points as possible.
This is the level with the most points to be collected in the game. However, it is also one of the few levels with an uncollectable score item: there is a book in the top left area of the level which cannot be reached, since the path to it is only one tile tall, and Keen is (approximately) two tiles tall. (Another level with an unreachable item, a lollipop, because of its height, is Capital City).
November Beta variations
The so called November Beta version of this level has some slight differences: The last part of the level near the exit, does not have all the Teddy Bears but a Tank Robot and a Garg instead.