You've seen Beijing's Water Cube, now get acquainted with the world’s latest amazing indoor sporting venue - Madrid's "Magic Box".

La Caja Magica is the city's largest building site, about 15 minutes south west of Madrid city centre, with 900 construction workers doing the necessary to make sure it opens on time in May.

It's the new home of the Madrid Masters tennis tournament which moves from autumn to spring in the 2009 calendar, becoming a combined ATP and WTA event, and BBC Sport has been allowed a peek behind the scenes.

It's going to be amazing.

The entire complex has a total of 16 clay courts but - here's the twist - three of them will be inside the same building, the Magic Box and, incredibly, all three will have independent retractable roofs.

So imagine the roof of a huge aircraft hanger - now press a button and one part of it opens to reveal a tennis stadium. Press a different button and another part of the roof opens above a totally different stadium.

The three courts are all close together but hi-tech soundproofing means a rock concert could be taking place inside one with a tennis match progressing next door, undisturbed.

And just like the Water Cube in China, the Olympic swimming venue, the Magic Box will come into its own at nightfall thanks to poly-bicorbonate walls with a 'see-through' effect.

Every seat in the building - 12,500 on the centre court alone - has an individual light beneath it. At night, the lights will shine upwards through the red plastic to create an extraordinary effect - basically a neon stadium shining through the see-through walls.

One for the cameras.

A second building stretches for 600 metres alongside the Magic Box. Ten practice courts will sit side by side in this new facility with the offices of the Spanish Tennis Federation in the middle.

Five thousand car park places sit on the other side of the complex linked to the buildings by a Wembley Way-style bridge which crosses a lake.

There appears to be an awful lot of work still to be done in six months but the pride shown by tournament director Manolo Santana, as he led the tour, left one in no doubt that hiccups would be avoided.

Promoter Ion Tiriac, the ebullient Romanian with such a passion for the future of tennis, has pulled off another masterstroke. In association with the city of Madrid, he's going to show off the world's top male and female players in the world's finest new tennis complex.

As long as those 900 builders keep at it for another six months, that is...