2521 Hallenbäder GmbH is a technical design and consultancy firm for the construction of new swimming pools with the 2521 approach from the Netherlands based on an initiative of the KNZB (Royal Dutch Swimming Federation) for the development of a cost-effective, yet high-quality, durable and multifunctional swimming pool. The basic idea is essentially to reduce the number of pools to a single pool, thereby significantly reducing both construction costs and operating costs. The name "2521" stands for the standard dimensions of a swimming pool (25 m long and 21 m wide).
