Durability plays a crucial role in maintaining the service life of a structure. This paper focuses on examining the durability of a building with a reinforced concrete structure that has been exposed to an offshore environment for 35 years. The study involved on-site inspections to assess external damage, including testing parameters such as the compressive strength of the concrete material and the overall tilt of the building. Additionally, microscopic inspection techniques, such as X-ray fluorescence (XRF), thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM), were employed to analyze the corrosion products and microstructure associated with the damage mechanism. Based on the data obtained from the on-site inspections, structural calculation software was used to calculate and verify the overall load-bearing capacity of the building, aiming to determine its safety level. The evaluation results revealed severe safety issues within the building, despite it not having reached its designed service life, particularly in relation to reinforcement corrosion.