The Floating Stadium of Singapore

Known as The Float at Marina Bay (or Marina Bay Floating Platform), this floating stadium is the world's largest floating stage. It is located on the waters of the Marina Reservoir, in Marina Bay, Singapore.
Made entirely of steel, the floating platform measures 120 metres long and 83 metres wide. It can bear up to 1,070 tonnes, equivalent to the total weight of 9,000 people, 200 tonnes of stage props and three 30-tonne military vehicles. The gallery at the stadium has a seating capacity of 30,000 people.
The stage took 13 months to build, and by April 2007, the platform and seating gallery were completed.
I think it's a great idea, but the grandstands seem to be quite far.

World First Vertical Ship SeaOrbiter

The world’s first space station of the sea “SeaOrbiter”, which is also the world’s first vertical ship will be built. The structure measures 51m (167ft) in height. It will be used mainly for research that allowing revolutionary view of life underwater and also be a useful tool for studying the link between global warming and the oceans.

The vertical ship was designed by the inventor Jacques Rougerie. It will use anti-collision system like the one used by the international space station
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Above the sea level, an upper lookout deck will raise 14 metre above the surface of the sea; there will be a tempoline deck with outdoor relaxation zone and an access deck for maintenance area, research zone, workshops and anticollison system.

Under the water level, there will be a service deck for kitchen, storage and showers, living area, laboratories and a pressurised deck for divers to undertake daily missions over a period of months.

When the SeaOrbiter does first set sail, there will be six crew members, six scientists and six more people on board - these may be astronauts
training in extreme conditions or doctors studying submarine human behaviour.

Here’s the image of the SeaOrbiter with its compartment.