Advanced space-based observing facilities continue to lower the resolution limit and detect solar coronal loops in greater detail. We continue to discover even finer sub-structures within coronal loop cross-sections in order to understand the nature of the solar corona. Here, we push this lower limit further to search for the finest coronal loop substructures, through taking advantage of the resolving power of the Swedish 1- m Solar Telescope (SST) / CRisp Imaging Spectro-Polarimeter (CRISP) together with co-observations from the Solar Dynamics Observatory (SDO) / Atmospheric Image Assembly (AIA). High resolution imaging of the chromospheric H-alpha 656.28 nm spectral line core and wings can allow one to deduce the topology of the local magnetic environment of the solar atmosphere where it is observed to form. We review the nature of coronal loop cross-sections at the finest scales through investigation of the flare-driven coronal rain phenomenon. We identify, through analysis of multiple data sets, large-scale and widespread evidence for catastrophic cooling in coronal loops and the existence of multi-thermal and multi-stranded sub-structures. Many cool strands even extend fully-intact from loop-top to foot-point. We find that coronal loop strands can appear 'bunched', with as many as 8 parallel cool strands, within the range of a relatively hot coronal loop cross-section. The strand number density vs. cross-sectional width distribution, as detected by CRISP, most-likely peaks at well below 100 km and currently 69% of the sub-structure strands are statistically unresolved in AIA coronal loops. The findings will be outlined in the context of future developments in instrumentation, such as with the construction of the 4-m DKIST facility, for observing coronal loops at even finer scales.