**5. Conclusions**

The presented study proves that in the case of a real structure with a limited possibility of dynamic excitation, reliable mode shape identification is a complex issue. Such a task demands the engagement of a few OMA techniques to authenticate the identified modal forms. The importance of the careful OMA inference is emphasized when the results are applied in the mathematical model of structural identification. The analysis provided the information concerning the mechanical parameters of the materials used in the considered lighthouse construction. The results complement the knowledge concerning such parameters for historic building materials.

**Author Contributions:** Conceptualization, A.T. and M.S.; Investigation, A.T., M.D. and M.S.; Methodology, A.T. and M.S.; Software, M.D. and M.S.; Validation, A.T. and M.D.; Visualization, M.D. and M.S.; Writing—original draft, A.T. and M.D.; Writing—review and editing, A.T., M.D. and M.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors express a great gratitude to Stefan Jacek Michalak, the owner of the lighthouse, for the consent to measurements and providing the technical documentation of the structure. Calculations have been partially made at the Academic Computer Centre in Gdansk TASK.

**Conflicts of Interest:** The authors declare no conflict of interest.
