This paper is part of an ongoing series of projects in which we are investigating 'threshold concepts': concepts that, among other things, transforms the way a student looks as the discipline and are often troublesome to learn. The word 'threshold' might imply that students cross the threshold in a single 'aha' moment, but often they seem to take longer. Meyer and Land introduce the term 'liminal space' for the transitional period between beginning to learn a concept and fully mastering it. Based on in-depth interviews with graduating seniors, we found that the liminal space can provide a useful metaphor for the concept learning process. In addition to observing the standard features of liminal spaces, we have identified some that may be specific to computing, specifically those relating to levels of abstraction.