The screenshot advertising [i]The Will of Crota[/i] [url=http://www.bungie.net/en/event/darkbelow]here[/url] is at the Forgotten Shore. I found the location based on it's scenery, and there is a spawn location (red vanguard flag) there.
The description (also [url=http://www.bungie.net/en/event/darkbelow]here[/url]) says that it takes place in the Jovian Complex. The Jovian Complex is behind a closed door that you can find by going through the Hive Seeder in the Skywatch. You can go from the Forgotten Shore to the Skywatch via the uphill road from the spawn location. (Path should look like [url=https://lh5.googleusercontent.com/-9-Iuy5Dq-qs/VGVMk6qccUI/AAAAAAAAApU/FAMcbkB6WuU/w1044-h558-no/Old_Russia_Map.png]this[/url].)
I expect that the Terrestrial Complex is around half of the strike; I don't think we hop right into the boss fight after that, but maybe we do. [url=http://static4.gamespot.com/uploads/original/1179/11799911/2708284-expansion+i_strike+shot+2.png]This[/url] picture Shows that the Jovian Complex isn't just a boss arena, but we can see Omnigul (the strike's boss) in the distance.
This leads me to believe the following possibilities:
1) Omnigul fights you throughout the entire Jovian Complex, trying to stop you from progressing.
2) Omnigul makes you chase her to her arena and there is a possible bonus for killing her before then.
3) You release Omnigul from some protection chamber and the entire Jovian Complex becomes the Arena.
4) There are multiple Omnigul battles, meaning that you have to defeat her multiple times and she runs off each time she losses too much of her health.
Thanks for reading :)