The Glenwood Hot Springs Pool’s claim to fame is that it’s the world’s largest outdoor mineral pool. At 405 feet long, with steam lifting from the water, the Yampah Spring-fed Grand Pool is larger than a football field. Still, there’s room to grow: Glenwood Hot Springs will open a collection of five new pools at the end of May, including a cold plunge, an infinity pool, and a hot spring pool with a waterfall feature. An architect’s rendering of part of the expansion to the Glenwood Hot Springs pools.