The Wikipedia page says
The Mundaneum was an institution created in 1910, following an initiative begun in 1895 by Belgian lawyers Paul Otlet and Henri La Fontaine, as part of their work on documentation science. It aimed to gather together all the world's knowledge and classify it according to a system they developed called the Universal Decimal Classification. Otlet and La Fontaine organized an International Conference of International Associations which was the origin of the Union of International Associations (UIA).
The Mundaneum has been identified as a milestone in the history of data collection and management, and as a precursor to the internet.