Radon can accumulate in underground areas such as show caves. Repairmen and tourist guides working in such caves may thus
be exposed to significant radiation doses. Therefore, it is necessary to measure the radon concentration to estimate the exact
radiation dose caused by radon. Considering that the radon concentration in caves usually shows significant seasonal fluctuations,
the monthly change of radon concentration was studied for 1 year in nine show caves opened to the public in Hungary. Despite
the fact that all of the caves were formed in karst rocks, the annual average radon concentration levels were rather different
between each other (541–8287 Bq m−3). The significant monthly fluctuation of the radon concentration indicates that the annual average radon concentration in
caves can only be accurately obtained by year-long measurements.