What do you think is inside this building?

It's OCEANDOME in Japan

When the roof is closed, you still get blue sky and puffy white clouds ... . .

Imagine a beach where the sky is always blue, it's never too hot or cold, the water isn't filled with salt and pollution, and the surf is always perfect - welcome to Ocean Dome, the world's only indoor beach.

Ocean Dome has its own flame-spitting volcano, crushed white marble "sand", and it also boasts the world's largest retractable roof, providing a permanently blue sky. Temperature, wind and humidity are closely controlled to provide an ultra-safe "sea-side" experience.

Every hour, the volcano erupts and the hi-tech wave machines start up, starting a few minutes of sanitized surfing.

Entrance cost is US$50 per person, which seems especially expensive given that there is a free, natural beach only 300 metres away.