"After looking through various data of the Sega Dreamcast Loop Checker disc, there were 2 BMP files that caught my attention. They look like the beta screenshots of Windy Valley from the Dreamcast version of Sonic Adventure. What do you think?
(Click for a larger picture)
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These are indeed prototype Windy Valley images, as the layouts match some of the more poor quality screenshots shown in videos of the earlier builds of the game.