As cultural heritage collections become available online they carry the promise of ‘access’ – new audiences, new uses, new understandings. But access is never simply open. Limits are imposed, structures are defined, categories are created. Decisions are made about what gets digitised and why. This chapter will describe a series of experiments within online cultural heritage collections to investigate the meaning of access. What happens, for example, if we invert the usual processes of discovery and focus on records in the National Archives of Australia that have been withheld from public view? What does our history look like if we restrict our gaze only to resources that have been digitised? By manipulating the contexts of cultural heritage collections we can start to see their limits and biases. By hacking heritage we can move beyond search interfaces and image galleries to develop an understanding of what’s missing.