From 1903-1913, the Beurs van Berlage housed the Amsterdam Stock Exchange. The exchange traded not only stocks, but also government bonds.
How do bonds work? It's a tradable loan to a national government or other public entity or to a company. Throughout the bond's duration, you receive annual interest payments. And at the end of a bond's duration, you'd get the full amount of the bond reimbursed. However, there is a large variety of bonds and in those days some even lasted forever. Others were reimbursed to some borrowers, while other borrowers to the same lender could keep their bonds and continue to benefit from dividends. It was decided by a lottery whose bonds would be reimbursed. And this was decided in the lottery room, our 'Lotenzaal'.