We provide continuous bihourly temperature and humidity data (November 2019 to March 2021) of four caves and three blowholes from arid and one of the largest contiguous karst areas in the world, the Nullarbor Plain in south Australia. The data were recorded with ten TGP-4500 Tinytag Plus 2 self-contained temperature (resolution ±0.01°C or better with reading range from -25°C to +85°C) and relative humidity (resolution ±3.0% or better with reading range from 0% to 100%) data loggers, and are available in a spreadsheet form. We also provide reported (but rare) visits to the caves, so that the data for particular day and/or hour can be treated as anthropogenically influenced. The data have great potential to provide insight into karst underground processes, air mass movements, hydrogeology, speleothems and (palaeo)climate, current climatic changes, and biology.Additional funding: Australian Speleological Federation Karst Conservation Fund (https://www.caves.org.au/conservation/karst-conservation-fund).