Within the project NestBox, we have developed a low cost sensor platform for measuring air quality, thermal comfort and other environmental parameters in the city. By measuring these parameters we can assess the quality of life in the city. The sensor platform contains various sensors to measure the air parameters (temperature, humidity, histogram), air quality (NO2, O3, CO, SO2, PM2.5, PM 10), solar radiation, and sound pollution, which will allow us to monitor the overall quality of the environment in which the citizens live. As part of the project, we want to build a reference telecommunication infrastructure for connecting a wide range of Smart City sensors based on the new wireless technologies such as LoRaWAN, LTE-M and 5G. In addition to the sensor platform, a cloud platform was developed where data is collected and processed. On the cloud platform, the data is freely accessible to the general public for the purpose of raising awareness and research. In the future, the platform will also specify open-source application interfaces APIs that will enable us to collect additional data in the city (traffic, energy, water supply, various services, opening times, etc.), which will be the basis for the so-called Slovenia Open Data platform (based on NYC Open Data). We firmly believe that publicly available data and open interfaces are a prerequisite for building modern Smart Cities.