The participants (except invited lecturers) are asked to book their accommodations by their own; one possibility is through the travel agency Kompas Postojna.
You can find many options here visitpostojna.si
28th International Karstological School "Classical karst"
Regional Karstology – Local And General Aspects (Postojna, June 14th–18th 2021) Within International Year of Karst and Caves