The core activity of Zumstein & Marques AG encompasses two main areas: 1. **Construction Company**: The company offers services in the construction sector, including project consulting, planning and implementation of construction projects. 2. **Gastronomy**: Zumstein & Marques AG is also active in the gastronomy sector and offers services such as the implementation of gastronomic concepts and consulting for gastronomic companies. Overall, the core activity of the company can be described as **Construction and Gastronomy Services**.