>>715654004
obligatory post mentioning naissancee

NaissancE was one of those games posted a bunch of webm threads and I guess it's more sci-fi brutalism than urban exploration, but it does feature very, very large environments that you can check out.
It's a shame that the game itself is kinda ass. The puzzles are not great and the weird breathing mechanic is not engaging. But, you can open up the console and fly around the map and just explore it. It is legit huge.