Dubai is set to welcome roughly 70 million tourists to its first World Expo. The event will be housed inside a gigantic, brand new, solar powered city. The cost to do build it? $7 billion.

Dubai beat out Ekaterinburg, Izmir, and São Paulo to host the World Expo in 2020. The project is looking optimistic too. It could add as many as 200,000 jobs and boost the city's GDP by one percent every year until 2020.

But like so many other cities that have hosted Expos, Olympics and World Cups, the ROI for these events aren't always what it's projected to be.

According to Reuters, the bid itself has driven up speculation in the Dubai property market with prices up 20 percent in the last year. But the whole project will come with a cost of between $7 and $9 billion over the next seven years.

All that money is going to 45,000 new hotel rooms, an extension of the city's subway system, with roads, tunnels, and other infrastructure investments and the 12.9 million square feet of exhibition space, designed by the Dubai office of American architecture firm HOK, which worked alongside a design team from Populous:

There will more than 150 countries setting up shop during the expo inside what architects describe as "innovation pods" and "best practices areas".