Researchers mostly concentrate on modelling the walking induced dynamic loading on the light-weight structures like pedestrian bridges, grandstands or slender floor slabs. This paper analyses the slender observation towers’ response to visitors’ ascending or descending induced dynamic loads analytically and experimentally. Presented critical range of the tower’s frequencies when the dynamic assessment is necessary to assure acceptable accelerations regarding visitors comfort. This is a topical in the locations where seismic design is not required and wind conditions are relatively mild which results in very slender and light-weight structures.