This is the world's deepest pool. It's called Y-40 and from the top it looks like a hole into the underworld.
Located at the Hotel Terme Millepini in Italy the pool is a playground for SCUBA divers, snorkeling fans and freedivers and includes a large top pool with caves and tunnels and then at the bottom there's a 40-metre straight drop down a tunnel.
To try and make the descent as pleasant as possible pool is filled with 4,300 cubic metres of spa water and kept to a very enjoyable 32-degrees.
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It was finally completed earlier this year and will be used for people to explore and also for training purposes helping freedivers increase their lung capacity in a safe, controlled environment.