The Clocktower is one of the later areas you unlock after clearing enough levels and obtaining enough keys. It can be found at the upper right corner door inside the Dungeon Area. Once you complete all 24 Clocktower stages this achievement will unlock. The Clocktower has any stages where you must use a rope and wrap it around cogs in order to create pathways. Simply walk up to the purple boxes and hit R-Trigger to get the rope. There will be some cases will you must cut the rope by making the rope touch some spikes too just like some Co-Op stages.
There is a video guide below of each level if you get stuck.