I was trying to think of open world games that also do big internal environments and couldn't think of many. Unity had those huge palaces but they're absent in Syndicate. GTA V has very interiors and what exists are small or just empty spaces. Fay Cry 3 and 4 just has small interiors.
What am I missing?
Destiny has some pretty large interiors even though I don't know if Destiny would qualify as open world in most people's eyes.
In GTA V, does the underground subway system count?