The 1000 Genomes Project created what they defined as accessibilty masks for the pilot phase, phase one and phase three of the Project. Some other studies have similar files.
In phase three of the 1000 Genomes Project, using the pilot criteria 95.9% of the genome was found to be accessible. For the stricter mask created during phase three, 76.9% was found to be accessible. A detailed description of the accessibility masks created during phase three, the final phase of the Project, can be found in section 9.2 of the supplementary material for the main publication. The percentages quoted are for non-N bases.
While the above was generated on GRCh37, similar files were created on GRCh38 for the reanalysis of the 1000 Genomes Project data on GRCh38. HGSVC2 also have files listing regions of the genome that were not analysed.