A key emerging contributor to genome function is the architectural organisation of the cell nucleus. DNA is wrapped around histones to form nucleosomes, which are folded into chromatin fibres and looped into a structure that eventually becomes a three-dimensional chromosome. The rearrangements in chromatin structure that control DNA template access occur on a spatiotemporal scale that render them ‘invisible’ to live cell imaging. Thus, in recent work we probed chromatin compaction at the level of nucleosomes by fluorescence lifetime based microscopy of FRET between fluorescently labelled histones. Here we multiplex this methodology with single localization microscopy of histone post-translational modifications, to determine the molecular mechanism that regulates chromatin dynamics at a DNA damage site with unprecedented spatial resolution.