The Asian monsoon is one of the largest atmospheric flow systems on Earth affecting the livelihood of hundreds of millions of people. Intensive research has revealed evidence of major and commonly abrupt changes in the strength of the system during the most recent geological history. This groundbreaking evidence is largely based on precisely dated speleothem (cave) records. Although this monsoon archive now extends back 640,000 years without gaps, the key proxy parameter, the oxygen isotope composition of speleothem calcite, remains incompletely understood, greatly limiting its use a quantifiably monsoon proxy. Here we propose a threefold approach to tackle this long-standing research question by combining innovative laboratory techniques including: stable isotope analyses of fluid inclusions; microthermometry of fluid inclusions, and, precise determinations of 17Oexcess of the calcite. Although this research involves substantial risks as it enters unchartered territory it holds the prospect of paving the way towards disentangling the atmospheric precipitation and the local temperature effects and will provide temperature and humidity records across intervals of major climate changes. These analyses, carried out along the main flow path of the Asian monsoon from northern India to Southeast China will eventually also yield important new constraints for the next generation of isotope-enabled general circulation models.