The eponymous protagonist, Repton, is a lizard who crawls around an underground maze in a quest to find all the diamonds (some being held in safes, their release being triggered by finding and collecting a key.) There are also jigsaw puzzle pieces to collect, which eventually spell out the message "Repton 2 is ended".
There are no levels as such in Repton 2, instead 'transporters' move Repton between different screens which, subject to a number of restrictions, can be completed in any order desired. The entire game is in effect one very large level without passwords, meaning that it must be completed in one attempt.
Source: Wikipedia, "http://en.wikipedia.org/wiki/Repton_%28video_game%29," available under the CC-BY-SA License.