PM-10, PM-2.5 and PM-1.0 concentrations were measured over an 8 h period at sites both inside and outside the museum of Wawel Royal Castle in Cracow, Poland. Gross alpha (alpha) and beta (beta) activities seemed to vary across the particle size range with generally higher levels of activities in the PM-2.5 particle fraction, and higher activities in the PM-10 fraction, while both the highest and the lowest beta activities were found in PM-1.0 fraction. However, statistically there was no significant difference. The highly radioactive PM-1.0 fraction comprised mainly Pb-210 and the Pb-210 progeny, Bi-210 and Po-210, and can be attributed to anthropogenic sourced outdoor radioactive particles brought indoors by visitors. Pb-210 is considered to be a good tracer of secondary aerosols produced by gas-to-particle conversion. Inside the Museum, the highest level of gross alpha activity was detected in the PM-10 fraction, and was mainly due to the uranium isotopes (U-234, U-235 and U-238) and their daughter products (Ra-226, Th-232, Po-210 or Ra-224), and Cs-137. The minimum and maximum total indicative doses per 8 h are caused by Cs-137 and Th-232, respectively.