Interstitiel - start by opening one hint at a time to see if it's enough information
If you haven't found the Interstitiel-pillar, it is located at the northern part of the Campusarea near the main entrance. The position is marked by a red dot in the picture below.
The letters are E, F, I, and V. When put in the right order, the letters spell FIVE.
The answer to this riddle is therefore 5