Operational modal analysis for identifying dynamic parameters, together with finite element model updating algorithms, is a promising and powerful tool for detailed analysis of complex civil engineering structures. It is also an integral part of vibration-based methods in structural health monitoring. In this work, the identification of the dynamic parameters was performed based on output-only vibration data recorded in a testing campaign on a 36 m high steel structure used as an observation tower for tourists in Latvia. To correctly interpret the experimental results, a finite element model of the tower has been developed within the Ansys environment. The model updating is performed by adopting an artificial intelligence algorithm called Particle Swarm Optimization. The calibration is performed with the aim of obtaining a numerical model that simulates the real dynamic behaviour of the case study with high accuracy. The calibrated model can be used as a base for the development and design of the structural health monitoring system of the tower.