Underwater Hotel

I'm a little skeptical on the engineering side of things. It sure looks awesome, but I think the water pressure, even at a relatively shallow 20m depth, will be impossible to overcome unless you pressurize the inside (like a submarine). The current design appears to be open to the atmosphere (the entrance is via tunnel), which means the pressure on the inside will be normal, while the pressure outside the walls will be tremendous.

Currently under construction in Dubai, Hydropolis is the world's first luxury underwater hotel. It will include three elements: the land station, where guests will be welcomed, the connecting tunnel, which will transport people by train to the main area of the hotel, and the 220 suites within the submarine leisure complex. It is one of the largest contemporary construction projects in the world, covering an area of 260 hectares, about the size of London's Hyde Park.