Researchers from the Institute of Oceanology of Bulgarian Academy of Sciences marked International Black Sea Day with an Open Day initiative in Varna and Sofia. Schoolchildren, students, and enthusiasts of marine science and nature met with marine researchers and had the opportunity to learn more about the challenges facing the Black Sea. Marine measuring systems by using an Argo floats were demonstrated at the Bulgarian Academy of Sciences, and the Institute of Oceanology. Students and visitors were introduced to the Argo float, what it is, how it works, what data is collected and what it is used for. The “Journey with the Ocean Observers” comic book booklet were given as gifts to the children who visited the events.