Every game starts from nothing, whether it's a massive spectacle like Uncharted: The Lost Legacy or a smaller independent production like Tacoma. In fact, one of the basic building blocks of game development is exactly that: blocks. When a level designer is conceptualizing a stage for players, they're often working without many of the aesthetic tools that help breathe life into it.
#Blocktober is a Twitter hashtag where developers are sharing intimate, unfinished looks at levels they've worked on. It's fascinating insight into the parts of game development most of us never see; often, publishers assume audiences can't handle seeing a game before layers of polish have been applied.
(Given the way some parts of the Internet react, I can't exactly blame them.)
You can sift through #Blocktober yourself—or follow @BlocktoberLD, which is retweeting entries in the hashtag—but I've pulled out some illuminating entries, and placed them beside finalizeds version of the levels being highlighted.