Every year, Valve hosts a giant gaming event called “The International”. While the prize pool is still being increased through purchases of the The International 2016 Battle Pass DLC bundle, it currently rests just below $19.4 million USD. The way previous years worked is that about a third went to first place, and the rest trickled down. Keep in mind that DOTA 2 is a team sport, though, so winnings don't all go to a single person.
Anywho, it will be a five-day event broadcasted on Twitch, Steam Broadcasting, WatchESPN, and YouTube. Owners of a SteamVR-compatible headset will also be able to view the broadcast in VR (which isn't just for The International, but this is the first The International to support it). It's not just projecting you into the stadium, either; it gives you a command center to see stats around you, or you can jump down into the map to see the battle around you “human scale”.
The International 6 begins on Monday.